Structure and isomer questions

Mark scheme

Examiner's comment

The majority of candidates were able to link movement of electrons to the ability of magnesium to conduct electricity. However, sometimes ‘electrons carry charge’ was not developed to explicitly state that they are mobile. Many diagrams were unclearly drawn and unlabelled, with the charge of the Mg2+ ion incorrectly shown.

Notes from the mark scheme and report

• regular arrangement of labelled Mg2+ ions (DO NOT ALLOW + or 3+
• DO NOT ALLOW nuclei/protons/positive atoms)
• electrons labelled and described as delocalised
• idea of electron movement required
• DO NOT ALLOW ions can move
• IGNORE 'electrons are free'

Mark scheme

Examiner's comment

The majority of candidates scored 2 or 3 marks on this question. Occasionally some gave carbonyl structures for E and G failing to recognise that full oxidation would take place. Other errors were additional H atoms (especially on the carbonyl carbon for D) or too many carbon atoms for E. A more common error was incorrect connectivity for the OH group especially in the carboxylic acid from alcohol G. This question was a good discriminator. Question 25 (b Just under half of candidates scored this with a wide range of incorrect responses. Most candidates did not appreciate that in order to form two isomeric alkenes a secondary alcohol was necessary, so that water could be eliminated from either side of the OH group.

Notes from the mark scheme and report

• reflux so primary alcohols E and G give carboxylic acids
• D gives the ketone
• F (tertiary) no reaction
• take care with branching for E
• penalise –HO connectivity once

Mark scheme

Examiner's comment

ocr.org.uk/science Oxford Cambridge and RSA CHEMISTRY A OCR Level 3 Advanced Subsidiary GCE in Chemistry A H032 For first teaching in 2015 Examiners’ report Version 1 H032/01 Summer 2025 series AS LEVEL Contents Contents ................................................................................................................................................... 2 Introduction .............................................................................................................................................. 4 Paper 1 series overview ........................................................................................................................... 5 Section A overview ................................................................................................................................... 6 Question 1 ............................................................................................................................................ 6 Question 2 ............................................................................................................................................ 7 Question 3 ............................................................................................................................................ 7 Question 4 ............................................................................................................................................ 8 Question 5 ............................................................................................................................................ 8 Question 6 ............................................................................................................................................ 9 Question 7 ............................................................................................................................................ 9 Question 8 .......................................................................................................................................... 10 Question 9 .......................................................................................................................................... 10 Question 10 ........................................................................................................................................ 11 Question 11 ........................................................................................................................................ 11 Question 12 ........................................................................................................................................ 12 Question 13 ........................................................................................................................................ 12 Question 14 ........................................................................................................................................ 13 Question 15 ........................................................................................................................................ 14 Question 16 ........................................................................................................................................ 15 Question 17 ........................................................................................................................................ 15 Question 18 ........................................................................................................................................ 16 Question 19 ........................................................................................................................................ 16 Question 20 ........................................................................................................................................ 17 Section B overview ................................................................................................................................. 18 Question 21 (a) ................................................................................................................................... 18 Question 21 (b) ................................................................................................................................... 19 Question 21 (c) ................................................................................................................................... 20 Question 21 (d) (i) ............................................................................................................................... 21 Question 21 (d) (ii) .............................................................................................................................. 23 Question 22 (a) .................................................................................................................................. 24 Question 22 (b) (i) .............................................................................................................................. 25 Question 22 (b) (ii) ............................................................................................................................. 25 Question 22 (c) ................................................................................................................................... 26 Question 23 (a) .................................................................................................................................. 27 Question 23 (b) ................................................................................................................................... 28 Question 23 (c) .................................................................................................................................. 29 Question 24 (a) (i) ............................................................................................................................... 30 Question 24 (a) (ii) .............................................................................................................................. 30 Question 24 (b) .................................................................................................................................. 31 Question 24 (c) (i) ............................................................................................................................... 32 Question 24 (c) (ii) .............................................................................................................................. 33 Question 25 (a) .................................................................................................................................. 34 Question 25 (b .................................................................................................................................... 35 Question 25 (c) ................................................................................................................................... 36 Introduction Our examiners’ reports are produced to offer constructive feedback on candidates’ performance in the examinations. Question 25 (b Just under half of candidates scored this with a wide range of incorrect responses.

Mark scheme

Examiner's comment

Approximately half of the candidates did not score any marks for this question. Many left the OH group on the alkenes formed i.e. removed H2 rather than H2O. Some attempted to draw cis/trans isomers with structures with no C=C in them. Some drew any alkene, e.g. but-2-ene, to show cis/trans, but this was not given here. Common reasons for scoring 1 mark included the isomers being the wrong way round or poor connectivity to -COOH groups.

Notes from the mark scheme and report

• dehydration gives HOOCCH=CHCOOH
• one mark if both stereoisomers shown in wrong columns
• DO NOT ALLOW incorrect connectivity to COOH (first occasion only)

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects

Mark scheme

Examiner's comment

Most candidates scored both marks here. Some lost a mark due to slips in naming, e.g. missing ‘di’ from dimethylpropane or incorrect numbering, e.g. 2-dimethylpropane, 2,3-dimethylpropane. Some used structural formula rather than skeletal. Common incorrect structures included cyclopentane, 1- or 2- ethylpropane or 1,2-dimethylpropane (not realising that these are 2-methylbutane) or 6 C structures with addition of a methyl group to pentane.

Notes from the mark scheme and report

• (2-)methylbutane and (2,2-)dimethylpropane
• structures must be skeletal
• all 4 points for 2 marks
• numbers if given must be correct
• DO NOT ALLOW methy/meth/methly

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects

Mark scheme

Examiner's comment

Candidates need to be reminded to check structures carefully – common errors included additional H atoms around C=C or missing the -CH3 group. Some used -C4H9 rather than writing out the complete structure; unfortunately, this is ambiguous so didn’t score the mark. Lower-attaining candidates some- times gave an alkane rather than an alkene, reacting with Br2 in presence of UV. Many had the correct reagents but added additional incorrect reagents resulting in loss of the mark, e.g. the addition of H2SO4 as a catalyst alongside NaOH for stage 2.

Notes from the mark scheme and report

• alkene X is 4-methylpent-1-ene (check number of H and CH3 branch)
• Stage 1 Br2
• Stage 2 NaOH/KOH(aq) (ALLOW H2O but DO NOT ALLOW steam)
• DO NOT ALLOW additional reagents
• IGNORE conditions and solvent

Mark scheme

Examiner's comment

This question required the candidates to identify the isomerism in an unfamiliar complex. This question was one of the more demanding ideas on the paper. A few candidates successfully drew the cis isomer and identified the type as cis/trans isomerism. Many candidates suggested, incorrectly, that the isomerisation was optical. A few did draw the cis complex ion but then identified the isomerism as optical.

Notes from the mark scheme and report

• draw the cis isomer (like groups on the same side of Cu)
• cis–trans (ALLOW geometric or E/Z)
• IGNORE charge and brackets

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects; M4.3 Understand the symmetry of 2-D and 3-D shapes

Mark scheme

Examiner's comment

Most candidates were able to score both marks here. However, a common error, which scored only 1 mark, was drawing the E and Z isomers the wrong way round, using the -CH3 groups to assign instead of considering priority. A common reason for losing both marks was by incorrectly copying the formula from the question, e.g. CH3CH- attached to C=C. Very few candidates gained no marks due to poor connectivity on the ethyl -CH2CH3 group connecting via CH3.

Notes from the mark scheme and report

• 1 mark if both isomers correct but in the wrong columns
• DO NOT ALLOW ethyl group bonded via CH3

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects; M4.3 Understand the symmetry of 2-D and 3-D shapes

Mark scheme

Examiner's comment

Most candidates managed to score 3 or 4 marks on this question. Some did not gain marks for structures without end bonds or for giving a complete unit of 2 molecules joined together. Some had only one repeat unit for each or gave more than two. Lower attaining candidates were often able to draw one type of polymer repeat unit but couldn’t do both. Polymer of 1-chlorobut-2-ene: Most were able to give the structure of two repeat units. Less successful candidates struggled to open the double bond and gave carbon chains with eight carbons in length connected to each other, sometimes with the C=C still present. In general, less successful candidates found it harder to get the marks for the addition polymer than with the condensation polymer, possibly as condensation polymerisation is taught later in the course. Polymer of 3-hydroxybutanoic acid: Very few didn’t gain a mark for showing the ester link between two monomers. A common error was adding -O- to both ends of the repeat unit. A few missed off Hs, particularly on C with CH3 attached. Most candidates knew the different types of polymerisations shown here. Some gave ‘alkene’ or ‘polyalkene’ rather than ‘addition’. A few gave ‘esterification’ or ‘substitution’ instead of condensation.

Notes from the mark scheme and report

• end bonds MUST be shown
• DO NOT ALLOW one or more than two repeat units (ECF in second structure)
• ester link shown
• addition AND condensation (DO NOT ALLOW 'additional')

Mark scheme

Examiner's comment

This mark was achieved by most candidates, with wrong answers largely linked to hydrogen bonding leading to hydrolysis rather than identifying the feature of the structure of this polymer that allows hydrolysis. Incorrect answers included: carboxylic acid, alcohol, hydroxyl, C-O bond (but not specific to ester).

Notes from the mark scheme and report

• ester link/group
• IGNORE reference to hydrogen bonding

Mark scheme

Examiner's comment

Many were able to identify that the -NO2 group is 3,5-directing as shown in both their explanations and the structure given. Only the highest attaining scored the mark for the explanation as it was necessary to suggest why synthesis 1 was successful as well as why synthesis 2 wasn’t. To do this, candidates had to deduce from synthesis 1 that -CH3 is 2,4-directing. Some suggested -NO2 or -CH3 was 1-directing. This, alongside structures showing the group next to the -NO2 group, suggests some confusion with how counting is achieved around the ring. It was also evident that some, although suggesting the -NO2 group is 3,5-directing, then drew a structure with the -CH3 in position 4. A few candidates suggested that CH3 ‘does not have a directing effect’ or ‘can direct anywhere on the ring’, presumably because it is not on the list of groups they need to know. Some candidates gave explanations based on reactivity, e.g. ‘the -NO2 group is electron withdrawing so makes the ring less reactive’, or that the -NO2 group itself would react with reagents used to add the methyl group, e.g. adding Cl to the ring instead.

Notes from the mark scheme and report

• CH3 is 2,(4)-directing AND NO2 is 3-directing
• IGNORE 'different directing effects' unless one is specified
• product is 3-nitromethylbenzene (mark scheme also shows a 3,5-disubstituted alternative)

Mark scheme

Examiner's comment

There were many excellent responses to this question requiring application of information that was provided. A lot of candidates scored both marks. Many less successful candidates were also able to correctly identify the correct organic products. Some candidates did not realise the COOH group formed the CO2 so often provided a second organic compound (usually propanone) from each reaction, as it contradicted the ketone they suggested. Some candidates struggle with skeletal formula, so marks were commonly lost for missing a C from the correct answer, e.g. pentan-2-one instead of pentan-3-one or butan-2-one rather than cyclopentone.

Notes from the mark scheme and report

• pentan-3-one and cyclopentanone
• IGNORE non-organic products such as CO2

Mark scheme

Examiner's comment

Most candidates were able to correctly draw the skeletal formula. Some candidates labelled the CH3 groups and OH connectivity was sometimes shown incorrectly as –HO or OH–. Other incorrect responses showed a main carbon chain with more, or less, than 6 carbon atoms or the CH3 side chains connected to the wrong carbon atoms. Good advice is to count the number of carbon atoms, with ‘hexan’ signifying 6 for this name.

Notes from the mark scheme and report

• must be skeletal (no CH3)
• check chain is 6 C
• DO NOT ALLOW OH–

Mark scheme

Examiner's comment

The structure of the amino acid was usually drawn correctly. The nickel complex ion provided problems with H2O connectivity and superfluous use of SO4. It was expected that bonds from Ni would be shown to the O atom, and that H2O was shown correctly in all orientations. So –H2O and –O2H were not allowed. Most candidates understood the importance of showing 3D bonds as wedges and the templates on the page will have helped in this respect. However, some candidates drew impossible 3D structures with bold wedges and dashed wedges shown opposite one another. Despite the overall charge being asked for in the question, a significant number of candidates omitted the charge.

Notes from the mark scheme and report

• B = CH3CH(NH2)COOH
• 2+ charge AND bonds to O of H2O
• DO NOT ALLOW –O2H

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects

Mark scheme

Examiner's comment

Over half the candidates found this question challenging an did not score the mark here. The most common error was to omit Structure C, but some also omitted Structure E. This suggested that many candidates may only apply the term ‘unsaturated’ to alkenes. It also highlights a potential lack of understanding of the delocalised ring in benzene and the relationship to the Kekulé structure.

Notes from the mark scheme and report

• B, C, D and E only (aromatic ring and C≡C count as unsaturated)

Mark scheme

Examiner's comment

The majority scored both marks here. A few drew the diacyl dichloride, but these were in the minority. A small minority only lost one mark, usually for incorrect connectivity on -OH groups. Some other errors seen included missing a carbon from alcohol, missing hydrogens on carbon if not drawn skeletally, carboxylic acid groups added directly on to the benzene ring with a pentavalent carbon atom or omitting the circle in the benzene ring.

Notes from the mark scheme and report

• benzene-1,4-dicarboxylic acid (or diacyl chloride) and butane-1,4-diol
• DO NOT ALLOW incorrect connectivity on OH

Mark scheme

Examiner's comment

Just over a quarter of candidates were able to gain all 4 marks. The successful candidates clearly identified where the ester and amide would be hydrolysed on the structure provided, helping them draw out the correct products. This question differentiated well. Most were able to gain some credit for hydrolysing the ester to give methanol and a carboxylate or carboxylic acid, leaving the amide bond and ring intact. However, some lost the first mark for giving the methoxide ion, assuming that the alkaline conditions are capable of deprotonating the alcohol group. Lower attaining candidates often broke other C-C bonds in the ring forming a range of products. A few displayed the structure as C=O-Na+ and some also protonated the amine group either with the ring intact or broken.

Notes from the mark scheme and report

• methanol (DO NOT ALLOW CH3O–Na+)
• carboxylate from ester/amide hydrolysis
• ring amide bond broken to give NH2
• final product is the dicarboxylate with NH2 (–COO–Na+ allowed)
• DO NOT ALLOW esters or amides remaining

Mark scheme

Examiner's comment

Most candidates were able to correctly recognise the correct direction for substitution, with over half gaining all 3 marks. Marks were most often lost for giving multiple substitution products despite being asked for the monosubstituted products. Many unnecessarily drew the same structures but with different orientations i.e. substituting on carbon-3 of a ring is the same as substituting on carbon-5.

Notes from the mark scheme and report

• CN is 3-directing: 3-chlorobenzonitrile only
• NHCOCH3 is 2- and 4-directing: two products
• IGNORE multisubstituted products and HCl
• Ensure students understand the term ‘monosubstituted’ and practise naming compounds to give the lowest possible numbering. This will also help them to recognise the equivalent structures.

Mark scheme

Examiner's comment

The diagrams and 3– charge were usually correct. The standard of 3D diagrams has improved over the years with most candidates using the wedges requirements outlined in the mark scheme. Some candidates often did not use wedges and their diagrams were not given marks. It should be noted that ‘impossible’ 3D diagrams showing wedges in unrealistic positions were also not given marks. Examples are shown in the published mark scheme.

Notes from the mark scheme and report

• overall 3– charge shown on at least one isomer
• bonds MUST go to the O– atoms of the ligands
• 3D wedges required
• DO NOT ALLOW simplified loop for ethanedioate
• MAX 2 for incorrect central element

Skills: M4.1 Use angles and shapes in regular 2-D and 3-D structures; M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects; M4.3 Understand the symmetry of 2-D and 3-D shapes

Mark scheme

Examiner's comment

Most candidates used the information in the question to draw a correct displayed formula of H3PO3. Another acceptable approach was to show a ‘dot-and-cross’ diagram. Candidates usually chose 104.5º for the P–O–H bond angles although a significant number suggested 180º. The O–P–O bond angle proved to be more difficult. Many suggested 120º by ignoring the lone pair of electrons on the P atom. The shape was analogous with NH3 giving a bond angle of 107º. Overall, candidates answered this question well. Candidates are advised to assess the number of bonded pairs and lone pairs around each atom when suggesting bond angles. This would have reduced the number of incorrect bond angles such as 180º for P–O–H and 120º for O–P–O.

Notes from the mark scheme and report

• P with 3 bonds only, each O bonded to P and H
• O–P–O = 107° (ALLOW 106–108)
• P–O–H = 104.5° (ALLOW 104–105)
• IGNORE geometry drawn

Skills: M4.1 Use angles and shapes in regular 2-D and 3-D structures; M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects

Mark scheme

Examiner's comment

Lots struggled here with just under half of candidates gaining no credit. Only the strongest responses recognised that a carbon-carbon double bond could be formed external to the ring from the methyl branch. A common error was repeating one of the first two isomers as a mirror or rotated image and so lost a mark - candidates need to be able to recognise same structures (especially using skeletal formula) Lower scoring candidates didn’t recognise this reaction would result in the elimination of water. So, it was common to see responses with three structures still containing the OH group or ketones (possible oxidation products), despite the molecular formula C7H10 being provided twice in the question. Some candidates attempted to give structural isomers of C7H10 that would not form from this reaction (see below) including those with smaller rings and even unsaturated straight chain compounds. Some even gave benzene structures. This question was particularly problematic to mark if previous structures drawn were then rubbed out. Drawing structures in exams Please remind candidates to draw structures clearly in black ink. If incorrect cross them out and redraw them. Drawing in pencil then rubbing out often leads to extra lines showing when exam papers are scanned making it appear that structures are incorrect.

Notes from the mark scheme and report

• both OH groups eliminated: two ring dienes and one with exocyclic C=CH2

Mark scheme

Examiner's comment

This was a demanding question with just over a third of candidates not scoring marks. However, many candidates were able to gain a mark for either showing the displayed ester or amide link between two benzene rings. Some candidates recognised that at least 3 PAS units would be needed to show both the amide and ester links appropriately. Few responses were able to show a section of polymer that contained correct amide and ester linkages, the correct substituent groups and at least one end bond. The most common reason why candidates did not secure all 3 marks was omission of the OH group on one or more benzene rings of PAS. This question was more challenging as candidates needed to show a polymer section. Many gave 2 ‘end bonds’ as they would for a repeat unit but this was not sufficient here due to the many different possible combinations, we could not make assumptions about what would be next. A common incorrect response was: Furthermore, many candidates just gave 1 benzene ring, like this:

Notes from the mark scheme and report

• displayed amide link and displayed ester link each between two benzene rings
• third mark dependent on both: at least one end bond and correct ring positions (C=O at 1, C–O at 2, C–NH at 4)

Mark scheme

Examiner's comment

Most candidates (more than half) were able to score both marks here, on what was a well-practised question from previous examination series. Most were able to identify the correct chiral carbon, with four different groups attached, and draw a 3-D representation of the two optical isomers with correct connectivity. Some candidates inadvertently drew the same structure (e.g. switched groups and gave a mirror image) so if not drawn in a standard way it needed extra checking. Some lost the second mark due to incorrect connectivity or use of C3H7. Some attempted to write formulae out as literal mirror images, e.g. 2(3HC)C and need to be told that this isn’t necessary as can sometime lead to connectivity errors.

Notes from the mark scheme and report

• four central bonds with at least two wedges
• mirror images with correct connectivity in both (bond to the CH of CH(CH3)2)
• ALLOW R or C3H7 for second mark only

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects; M4.3 Understand the symmetry of 2-D and 3-D shapes

Mark scheme

Examiner's comment

A significant number of candidates did not attempt this question despite similar questions appearing in previous exam series. However, approximately a quarter of candidates scored all 4 marks. Some lost the final mark for not protonating the amine groups as required as under acidic conditions. A very common error was to hydrolyse the amides to give acyl chlorides or even aldehydes rather than carboxylic acids. Lower scoring candidates often had incomplete hydrolysis or no hydrolysis at all with just changes to acid/amine/phenol functional groups, e.g. protonation of amine to form salts or swapping or OH groups for Cl. Candidates need to check their answers carefully for missing or extra Hs as this lost marks. It was much easier to mark candidates’ work presented with structures with a similar arrangement to compound E.

Notes from the mark scheme and report

• three amino acids from the two amide links
• 1 mark each with NH2 or NH3+
• fourth mark only if all three shown as NH3+ (acid conditions)
• ALLOW salts NH3+Cl–

Mark scheme

Examiner's comment

Most candidates did not seem to understand how to apply their knowledge of what an empirical formula should look like to this situation. Many giving the formula of the complex ion instead. Those candidates who were successful often had the incorrect overall charge on the ion with 3+ as the common error, not considering the 2 Cl- ligands. Conversely, most candidates did very well at representing the isomers of the complex. Most were able to use the wedge and broken line notation to suggest the geometry of what they were drawing. Although a small number drew the trans isomer in three different orientations, most correctly drew the trans and cis forms and managed to show the optical isomers – even when they did not make use of the top pair of answer boxes to assist them with their mirror images. Candidates are advised to focus on the mirror image and avoid subsequent rotations and inversions of the molecule. This can often lead to two of the same isomers being drawn. Candidates showed a good accuracy with their connectivity of the N atom.

Notes from the mark scheme and report

• empirical formula FeC4H16N4Cl2 with 1+ charge (DO NOT ALLOW Fe(NH2CH2CH2NH2)2Cl2)
• two cis mirror images and one trans
• correct wedges (2 out, 2 in, 2 in plane)
• Fe–N connectivity errors penalised once
• 1 mark if all three shown with Cl but no N

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects; M4.3 Understand the symmetry of 2-D and 3-D shapes

Mark scheme

Examiner's comment

This question required candidates to link their knowledge of cis and trans isomers with branched hydrocarbons. Higher ability candidates were able to do this. The majority of candidates scored 1 mark for correctly drawing cis and trans isomers of an unbranched hydrocarbon.

Notes from the mark scheme and report

• 4-methylpent-2-ene cis and trans (ALLOW 3-methylpent-2-ene in either box)
• C3H7 not sufficient (could be unbranched)
• 1 mark if in wrong boxes or for cis/trans of an unbranched C6H12

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects; M4.3 Understand the symmetry of 2-D and 3-D shapes

Mark scheme

Examiner's comment

This question discriminated well. Candidates were required to identify the groups around a chiral carbon and then draw the two corresponding optical isomers. Incorrect responses frequently had incorrect connectivity around the chiral carbon, bond angles of 180 or 2D structures.

Notes from the mark scheme and report

• C is 3-methylpent-1-ene
• four bonds to chiral C with wedges
• mirror images with correct connectivity
• DO NOT ALLOW a bond angle of 180°

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects; M4.3 Understand the symmetry of 2-D and 3-D shapes

Mark scheme

Examiner's comment

Most candidates were able to correctly draw the structure of D and E. Many candidates did not explain their answers in terms of the number of different hydrogen and carbon environments or the presence/ absence of a carbon-carbon double bond.

Notes from the mark scheme and report

• D is cyclohexane (all H and all C equivalent, no C=C)
• E is 2,3-dimethylbut-2-ene (all H equivalent, 2 C environments, C=C present)
• 1 mark for structures if in the wrong boxes

Skills: M4.3 Understand the symmetry of 2-D and 3-D shapes

Mark scheme

Examiner's comment

Most candidates were able to score 1 mark for correctly drawing the structures of the two aldehyde products of the first reaction. The second reaction proved more challenging, with most candidates incorrectly drawing two products.

Notes from the mark scheme and report

• BOTH structures required for each mark: propanal and ethanal from pent-2-ene
• a single open-chain dicarbonyl from the cyclic alkene

Mark scheme

Examiner's comment

This question proved difficult and discriminated well. Higher ability candidates correctly used SI units and showed each step of their calculation and then using this to correctly identify a structure of compound X. Candidates frequently used the wrong interconversions and gave structures that lacked a chiral centre. A small number of candidates used molar gas volume rather than PV=nRT for their calculation.

Notes from the mark scheme and report

• convert cm3 to m3 and °C to K
• M = 168 so C3H2F6O
• structure must contain F6O, C–O–C and a chiral carbon (DO NOT ALLOW no chiral carbon)
• use of 24 dm3 loses the calculation mark but ECF (171, C3H5F6O)

Skills: M0.0 Recognise and make use of appropriate units in calculations; M2.2 Change the subject of an equation; M2.3 Substitute numerical values into algebraic equations using appropriate units for physical quantities

Mark scheme

Examiner's comment

Most candidates were able to calculate the initial ratios and then use this to calculate the molecular formula, linking to the m/z peak at 58. The most common error seen was for the structures of F and G to the in the incorrect boxes, suggesting that candidates have not interpreted the fragment ions to work out F was the aldehyde.

Notes from the mark scheme and report

• C3H6O with evidence of 58 (molecular ion)
• F is propanal from fragment m/z 29 (CH3CH2+ or CHO+)
• G is propanone
• IGNORE m/z 15 (not unique) and 43

Skills: M0.2 Use ratios, fractions and percentages; M3.1 Translate information between graphical, numerical and algebraic forms

Mark scheme

Examiner's comment

Most candidates were given at least 1 mark with many correctly drawing the structure of pent-3-enoic acid. Common errors included drawing pent-2-enoic acid or propenoic acid, suggesting a lack of knowledge of prefixes. The second mark required candidates to draw two repeat units, frequently candidates tried to draw repeat units linking the carboxylic acid groups rather than identifying that it is the carbon-carbon double bond that breaks.

Notes from the mark scheme and report

• CH3CH=CHCH2COOH (E or Z)
• two repeat units with side bonds
• ECF only from pent-2-enoic or pent-4-enoic acid
• IGNORE brackets and n

Mark scheme

Examiner's comment

This question proved difficult for candidates with the majority of candidates not scoring the mark. A significant proportion of candidate had identified the monomer but drew structures that combined skeletal and displayed formulae. This resulted in ambiguous structures being given that had missing hydrogen atoms on the carbons. Drawing of organic structures Candidates need practice at drawing structures that are not ambiguous. They should check the number of bonds on each atom and make sure the appropriate number of hydrogen atoms are drawn.

Notes from the mark scheme and report

• single hydroxy-acid monomer containing both OH and COOH

Mark scheme

Notes from the mark scheme and report

• ALLOW any unambiguous skeletal, structural or displayed formula e.g. CF3CHClBr

Mark scheme

Notes from the mark scheme and report

• 2-bromo-2-methylpropane and 1-bromo-2-methylpropane
• ALLOW any unambiguous formula type

Mark scheme

Examiner's comment

Question 16(d)(ii): Many candidates did not correctly answer this question with products being given that had too few carbon atoms. .

Notes from the mark scheme and report

• cyclohexene ring with the two COOCH3 groups on adjacent carbons
• cyclohexa-1,4-diene with two adjacent methyl groups on a C=C from but-2-yne

Mark scheme

Notes from the mark scheme and report

• H2N(CH2)4NH2 and ClOC–C6H4–COCl
• amide link
• one repeat unit only with end bonds shown

Mark scheme

Notes from the mark scheme and report

• four bonds to chiral C with at least two wedges
• two structures that are mirror images with correct connectivity
• 1 mark if CH3 shown as R

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects; M4.3 Understand the symmetry of 2-D and 3-D shapes

Mark scheme

Notes from the mark scheme and report

• ibuprofen carboxylate COO–
• lysine with one NH3+ (either amine group protonated)
• IGNORE small slip in carbon chains

Mark scheme

Notes from the mark scheme and report

• 2.62 : 1.31 : 1.31 : 3.06 gives C6H3N3O7, linked to M = 229.0
• trinitrophenol
• 4 peaks = 4 carbon environments fits 2,4,6 or 3,4,5
• –OH 2,4-directing so 2,4,6-trinitrophenol
• no ECF from wrong molar ratio

Skills: M0.2 Use ratios, fractions and percentages; M3.1 Translate information between graphical, numerical and algebraic forms

Mark scheme

Examiner's comment

25(a) This part was generally well-answered with well-prepared candidates scoring all three marks. The most common errors resulted from the products of reaction with HBr. The same structure was often drawn, reversed in one of the boxes. Candidates should take care to check that the atoms in a structure have the correct number of bonds. Some candidates added HBr across the C=C double bond but left the C=C bond intact in their final structures, showing carbon atoms with 5 bonds instead of 4. 25(b) As with 25(a), this question rewarded the well-prepared candidate and discriminated well. Conversely, many mechanisms showed little resemblance to the accepted mechanism for electrophilic addition. Mechanisms were often seen showing curly arrows going in the wrong direction and between the wrong bonds and atoms, with incorrect charges and dipoles, and partial charges used where full charges were required. Many candidates were aware that members of a homologous series have the same functional group and react in similar ways. A second mark was available for stating that the formula of successive members increases by CH2. It is important to stress ‘successive’ in communicating this information. 25(c)(ii) This part required candidates to apply their understanding of a ‘general formula’ in a novel context. Many candidates analysed the provided formulae for the alkynes homologous series to derive the correct general formula of CnH2n–2. There was no real pattern in the incorrect responses which usually contained a mixture of numbers for the H atom, e.g. CnH2n, CnHn+1. 25(c)(iii) Although attempted by most candidates, comparatively few responses could be credited. The key to success was again to use the information provided: the formation of a saturated compound. The commonest response seen showed addition of 1 Br2 molecule to form the unsaturated CH3CBr=CHBr instead of the saturated CH3CBr2–CBr2 by addition of 2 Br2. This question was one of the most difficult on the exam paper. 25(c)(iv) Most candidates achieved 1 of the available 2 marks for drawing the structure of but-2-yne, CH3C≡CCH3. The structure of but-1-yne was then usually drawn in the other box despite it being provided already in the table at the start of part (c). A variety of creditworthy structures were seen, including H2C=CH– CH=CH2, cyclobutene and isomers of methylcyclopropane. 25(c)(v) It was encouraging to see the many correct structures drawn from the unfamiliar 2,5-dimethylhept-3-yne. Most candidates positioned the C≡C group and the two substituted CH3 groups correctly. The commonest error was showing a main stem with 6, rather than 7 C atoms. If any of your students’ results are not as expected, you may wish to consider one of our review of results services. For full information about the options available visit the OCR website. If university places are at stake you may wish to consider priority service 2 reviews of marking which have an earlier deadline to ensure your reviews are processed in time for university applications. Our priority is supporting you and your students this autumn and to support you as you prepare for summer 2021 exams. We’ll update our website information regularly with resources, guidance and key information. • Teachers • Students • Exams officers • Assessment specialists We are sending a weekly roundup to tell you about important updates. You can also sign up for your subject specific updates. If you haven’t already, sign up here. Attend one of our popular CPD courses to hear directly from a senior assessor or drop in to a Q&A session. All our courses for the academic year 2020-2021 are being delivered live via an online platform, so you can attend from any location. Please find details for all our courses on the relevant subject page on our website or visit OCR professional development. ExamBuilder is the question builder platform for a range of our GCSE, A Level, Cambridge Nationals, Cambridge Technicals and Functional Skills qualifications. See the full list of available qualifications in the sign up form. ExamBuilder is free for all OCR centres with an Interchange account and gives you unlimited users per centre. We need an Interchange username to validate the identity of your centre's first user account for ExamBuilder. If you do not have an Interchange account please contact your centre administrator (usually the Exams Officer) to request a username, or nominate an existing Interchange user in your department. Review of results

Notes from the mark scheme and report

• side bonds required on repeat unit
• DO NOT ALLOW more than one repeat unit
• IGNORE brackets and n
• both 1-bromopropane and 2-bromopropane required, either order

Mark scheme

Examiner's comment

25(a) This part was generally well-answered with well-prepared candidates scoring all three marks. The most common errors resulted from the products of reaction with HBr. The same structure was often drawn, reversed in one of the boxes. Candidates should take care to check that the atoms in a structure have the correct number of bonds. Some candidates added HBr across the C=C double bond but left the C=C bond intact in their final structures, showing carbon atoms with 5 bonds instead of 4. 25(b) As with 25(a), this question rewarded the well-prepared candidate and discriminated well. Conversely, many mechanisms showed little resemblance to the accepted mechanism for electrophilic addition. Mechanisms were often seen showing curly arrows going in the wrong direction and between the wrong bonds and atoms, with incorrect charges and dipoles, and partial charges used where full charges were required. Many candidates were aware that members of a homologous series have the same functional group and react in similar ways. A second mark was available for stating that the formula of successive members increases by CH2. It is important to stress ‘successive’ in communicating this information. 25(c)(ii) This part required candidates to apply their understanding of a ‘general formula’ in a novel context. Many candidates analysed the provided formulae for the alkynes homologous series to derive the correct general formula of CnH2n–2. There was no real pattern in the incorrect responses which usually contained a mixture of numbers for the H atom, e.g. CnH2n, CnHn+1. 25(c)(iii) Although attempted by most candidates, comparatively few responses could be credited. The key to success was again to use the information provided: the formation of a saturated compound. The commonest response seen showed addition of 1 Br2 molecule to form the unsaturated CH3CBr=CHBr instead of the saturated CH3CBr2–CBr2 by addition of 2 Br2. This question was one of the most difficult on the exam paper. 25(c)(iv) Most candidates achieved 1 of the available 2 marks for drawing the structure of but-2-yne, CH3C≡CCH3. The structure of but-1-yne was then usually drawn in the other box despite it being provided already in the table at the start of part (c). A variety of creditworthy structures were seen, including H2C=CH– CH=CH2, cyclobutene and isomers of methylcyclopropane. 25(c)(v) It was encouraging to see the many correct structures drawn from the unfamiliar 2,5-dimethylhept-3-yne. Most candidates positioned the C≡C group and the two substituted CH3 groups correctly. The commonest error was showing a main stem with 6, rather than 7 C atoms. If any of your students’ results are not as expected, you may wish to consider one of our review of results services. For full information about the options available visit the OCR website. If university places are at stake you may wish to consider priority service 2 reviews of marking which have an earlier deadline to ensure your reviews are processed in time for university applications. Our priority is supporting you and your students this autumn and to support you as you prepare for summer 2021 exams. We’ll update our website information regularly with resources, guidance and key information. • Teachers • Students • Exams officers • Assessment specialists We are sending a weekly roundup to tell you about important updates. You can also sign up for your subject specific updates. If you haven’t already, sign up here. Attend one of our popular CPD courses to hear directly from a senior assessor or drop in to a Q&A session. All our courses for the academic year 2020-2021 are being delivered live via an online platform, so you can attend from any location. Please find details for all our courses on the relevant subject page on our website or visit OCR professional development. ExamBuilder is the question builder platform for a range of our GCSE, A Level, Cambridge Nationals, Cambridge Technicals and Functional Skills qualifications. See the full list of available qualifications in the sign up form. ExamBuilder is free for all OCR centres with an Interchange account and gives you unlimited users per centre. We need an Interchange username to validate the identity of your centre's first user account for ExamBuilder. If you do not have an Interchange account please contact your centre administrator (usually the Exams Officer) to request a username, or nominate an existing Interchange user in your department. Review of results

Notes from the mark scheme and report

• any two of but-2-yne, buta-1,3-diene, buta-1,2-diene or cyclic C4H6 isomers
• ALLOW any unambiguous formula

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects

Mark scheme

Examiner's comment

25(a) This part was generally well-answered with well-prepared candidates scoring all three marks. The most common errors resulted from the products of reaction with HBr. The same structure was often drawn, reversed in one of the boxes. Candidates should take care to check that the atoms in a structure have the correct number of bonds. Some candidates added HBr across the C=C double bond but left the C=C bond intact in their final structures, showing carbon atoms with 5 bonds instead of 4. 25(b) As with 25(a), this question rewarded the well-prepared candidate and discriminated well. Conversely, many mechanisms showed little resemblance to the accepted mechanism for electrophilic addition. Mechanisms were often seen showing curly arrows going in the wrong direction and between the wrong bonds and atoms, with incorrect charges and dipoles, and partial charges used where full charges were required. Many candidates were aware that members of a homologous series have the same functional group and react in similar ways. A second mark was available for stating that the formula of successive members increases by CH2. It is important to stress ‘successive’ in communicating this information. 25(c)(ii) This part required candidates to apply their understanding of a ‘general formula’ in a novel context. Many candidates analysed the provided formulae for the alkynes homologous series to derive the correct general formula of CnH2n–2. There was no real pattern in the incorrect responses which usually contained a mixture of numbers for the H atom, e.g. CnH2n, CnHn+1. 25(c)(iii) Although attempted by most candidates, comparatively few responses could be credited. The key to success was again to use the information provided: the formation of a saturated compound. The commonest response seen showed addition of 1 Br2 molecule to form the unsaturated CH3CBr=CHBr instead of the saturated CH3CBr2–CBr2 by addition of 2 Br2. This question was one of the most difficult on the exam paper. 25(c)(iv) Most candidates achieved 1 of the available 2 marks for drawing the structure of but-2-yne, CH3C≡CCH3. The structure of but-1-yne was then usually drawn in the other box despite it being provided already in the table at the start of part (c). A variety of creditworthy structures were seen, including H2C=CH– CH=CH2, cyclobutene and isomers of methylcyclopropane. 25(c)(v) It was encouraging to see the many correct structures drawn from the unfamiliar 2,5-dimethylhept-3-yne. Most candidates positioned the C≡C group and the two substituted CH3 groups correctly. The commonest error was showing a main stem with 6, rather than 7 C atoms. If any of your students’ results are not as expected, you may wish to consider one of our review of results services. For full information about the options available visit the OCR website. If university places are at stake you may wish to consider priority service 2 reviews of marking which have an earlier deadline to ensure your reviews are processed in time for university applications. Our priority is supporting you and your students this autumn and to support you as you prepare for summer 2021 exams. We’ll update our website information regularly with resources, guidance and key information. • Teachers • Students • Exams officers • Assessment specialists We are sending a weekly roundup to tell you about important updates. You can also sign up for your subject specific updates. If you haven’t already, sign up here. Attend one of our popular CPD courses to hear directly from a senior assessor or drop in to a Q&A session. All our courses for the academic year 2020-2021 are being delivered live via an online platform, so you can attend from any location. Please find details for all our courses on the relevant subject page on our website or visit OCR professional development. ExamBuilder is the question builder platform for a range of our GCSE, A Level, Cambridge Nationals, Cambridge Technicals and Functional Skills qualifications. See the full list of available qualifications in the sign up form. ExamBuilder is free for all OCR centres with an Interchange account and gives you unlimited users per centre. We need an Interchange username to validate the identity of your centre's first user account for ExamBuilder. If you do not have an Interchange account please contact your centre administrator (usually the Exams Officer) to request a username, or nominate an existing Interchange user in your department. Review of results

Notes from the mark scheme and report

• ALLOW any unambiguous combination of skeletal, structural or displayed formula

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects

Mark scheme

Notes from the mark scheme and report

• four bonds to the chiral C with at least two wedges
• two structures must be mirror images with correct connectivity

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects; M4.3 Understand the symmetry of 2-D and 3-D shapes

Mark scheme

Notes from the mark scheme and report

• B undergoes addition (dichloro product), C undergoes substitution on the ring

Mark scheme

Notes from the mark scheme and report

• ester link must be displayed
• end bonds MUST be shown
• DO NOT ALLOW more than one repeat unit
• IGNORE brackets and n

Mark scheme

Notes from the mark scheme and report

• methanol plus two amino acids
• both amino acids must show NH3+ for full marks (acid conditions): 2 of 3 if NH2/NH3 without charge

Mark scheme

Examiner's comment

1a(i) Most candidates labelled some of the apparatus correctly and identified the reflux technique. A significant number showed water flowing in the wrong direction and ‘distillation’ was given as the name of the technique. The ‘condenser’ was sometimes labelled incorrectly, e.g. ‘condensation tube, ‘distillation tube’ and ‘water jacket’. Only just over half the candidates were given both marks. 1a(ii) Many diagrams were incomplete and it was comparatively rare for both of the two available marks to be given. Important labels were often missing. Some candidates drew diagrams of other techniques, such as distillation. Many responses were not credited with marks and this question was often omitted. Candidates need practice in recognising practical techniques and in drawing acceptable diagrams. 1b(i) Candidates were expected to explain the different boiling points of three amines. Most candidates linked increased branching with less surface contact between molecules, leading to weaker induced dipole interactions (London forces). Fewer candidates linked the decreasing boiling points to less energy being required to break the intermolecular bonds. The highest performing candidates recognised the large difference between the boiling points of the primary and tertiary amines. They then identified the cause: primary amines form hydrogen bonds but tertiary amines do not. This question was answered reasonably well with fewer candidates than in the past describing relative strengths of covalent bonds, a common misconception. 1(b)(ii) Most candidates rearranged the ideal gas equation correctly to make n the subject. They then substituted correct values for p, V, R and T into the equation, with correct unit conversions. Most candidates then calculated n correctly as 2.32 × 10–3 and combined this value with the mass of 0.202 g to derive the molecular formula as 87. Lower-attaining candidates often made an error in their conversion of cm3 into m3, by multiplying by 10–3 rather than 10–6. This error resulted in a value of n as 2.32 and the unrealistic molecular mass of 8.7 × 10–3, from which a molecular formula is impossible. Candidates in this position are advised to check back at the unit conversions in the working. Very few candidates did not convert 100ºC into 373 K. Candidates with the correct molecular formula of 87 usually suggested C5H13N as the molecular formula. A significant number quoted C5H11NH2. This response was not credited as it is not a ‘molecular’ formula. There are several possible structures of C5H13N with three 13C NMR peaks and any were credited. Error carried forward was applied from a different molecular mass for both the molecular formula and a structure. This emphasises the importance of working within calculation; credit will always be given for a correct method. Instead of using the ideal gas equation, some candidates used the molar gas constant at room temperature and pressure, 24.0 dm3, which gives a molecular mass of 67. This simplified approach could only gain the final 2 marks for this question: a molecular formula (with an error carried forward value of 67, e.g. C4H5N) and a structure of an amine with this molecular formula and 3 peaks in the 13C NMR spectrum. 1(c) Candidates were supplied with information about an unfamiliar reaction of an amino acid and asked to predict a possible equation. Many candidates suggested H2O as one product, being the difference in the formula of the amino acid and the C3H3NO cyclic organic product. Any cyclic structure of C3H3NO that met the bonding rules for C, H, N and O was credited. Examples included a 4-membered ring lactam and substituted cyclopropenes. A significant number of candidates showed an equation for the reaction of two molecules of the amino acid to form 2 H2O and a cyclic dipeptide. Although chemically feasible, the dipeptide could not be credited because the molecular formula was C3H3NO in the question. This error could have been avoided if the information in the question had been used.

Notes from the mark scheme and report

• n = pV/RT with V = 72.0 × 10^-6 m3 and T = 373 K gives M = 87 so C5H13N
• structure must have 3 carbon environments
• use of 24 000 (not RTP) limits to 3 marks by ECF (M = 67.3, C4H5N)

Skills: M0.0 Recognise and make use of appropriate units in calculations; M2.2 Change the subject of an equation; M2.3 Substitute numerical values into algebraic equations using appropriate units for physical quantities; M3.1 Translate information between graphical, numerical and algebraic forms

Mark scheme

Examiner's comment

AS LEVEL CHEMISTRY A Examiners’ report H032/01 Summer 2019 series Version 1 H032 For first teaching in 2015 www.ocr.org.uk/science Contents Introduction .............................................................................................................................................. 4 Paper 1 series overview ........................................................................................................................... 5 Section A overview ................................................................................................................................... 6 Question 2 ............................................................................................................................................ 6 Question 4 ............................................................................................................................................ 6 Question 5 ............................................................................................................................................ 7 Question 6 ............................................................................................................................................ 7 Question 9 ............................................................................................................................................ 8 Question 10 .......................................................................................................................................... 9 Question 11 ........................................................................................................................................ 10 Question 12 ........................................................................................................................................ 10 Question 14 ........................................................................................................................................ 11 Question 15 ........................................................................................................................................ 11 Question 17 ........................................................................................................................................ 12 Question 18 ........................................................................................................................................ 13 Question 19 ........................................................................................................................................ 13 Question 20 ........................................................................................................................................ 14 Section B overview ................................................................................................................................. 15 Question 21 (a) ................................................................................................................................... 15 Question 21 (b) .................................................................................................................................. 15 Question 21 (c) ................................................................................................................................... 16 Question 21 (d) (i) ............................................................................................................................... 16 Question 21 (d) (ii) .............................................................................................................................. 17 Question 21 (d) (iii) ............................................................................................................................. 18 Question 21 (d) (iv) ............................................................................................................................. 19 Question 22 (a) (i) ............................................................................................................................... 20 Question 22 (a) (ii) .............................................................................................................................. 20 Question 22 (b) ................................................................................................................................... 21 Question 22 (c) ................................................................................................................................... 22 Question 23 (a) ................................................................................................................................... 23 Question 23 (b) ................................................................................................................................... 24 Question 24 (a) (i) ............................................................................................................................... 25 Question 24 (a) (ii) .............................................................................................................................. 25 Question 24 (b) (i) ............................................................................................................................... 26 Question 24 (b) (ii) .............................................................................................................................. 27 Question 25 (a) (i), (ii) and (iii) ............................................................................................................ 28 Question 25 (b) (i) ............................................................................................................................... 29 Question 25 (b) (ii) .............................................................................................................................. 29 Question 25 (b) (iii) ............................................................................................................................. 30 Introduction Our examiners’ reports are produced to offer constructive feedback on candidates’ performance in the examinations. Question 25 (a) (i), (ii) and (iii) Part 25(a)(i) discriminated extremely well and rewarded well-prepared candidates.

Notes from the mark scheme and report

• reflux so primary alcohol A gives the carboxylic acid
• tertiary alcohol B gives NONE
• DO NOT ALLOW 'sticks' in structures

Mark scheme

Examiner's comment

This was well answered by most candidates

Notes from the mark scheme and report

• CH3C(CH3)ICH2CH3
• any unambiguous formula

Mark scheme

Examiner's comment

The drawing of simple 3-D diagrams of relevant shapes is a skill that is assessed in A Level chemistry. Common errors are listed in the exemplars. Some candidates drew in pencil then over-wrote in ink. Candidates need to remember that the scanned image does not differentiate between pencil and ink, so it is not necessary for them to do this. Candidates should avoid incorrect connectivity between the ligand and the central metal ion. Candidates should be taught which atom within the ligand supplies the lone pair to form the coordinate bond. In this case oxygen has lone pairs, not hydrogen as suggested by the candidate in the bonding involving the bottom left hand ligand.

Notes from the mark scheme and report

• 3– charge
• must show 2 out wedges, 2 in wedges and 2 in plane (or 4 lines + 1 out + 1 in)

Skills: M4.1 Use angles and shapes in regular 2-D and 3-D structures; M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects

Mark scheme

Examiner's comment

This question, which discriminated well, required candidates to apply their knowledge of stereoisomerism to geraniol and citronellal. The majority of responses focused on E/Z isomerism, as shown in Exemplar 2. Many candidates were able to show the structure of the Z isomer of geraniol and scored at least one mark. Stronger responses were able to explain this type of isomerism as the result of the carbon-carbon double bond between carbon atoms 2 and 3. Common errors included attributing E/Z isomerism to the double bond between carbon atoms 6 and7 or use of cis/trans to describe the isomers (the latter of which was ignored by the mark scheme as it does not apply to geraniol). The best responses also identified the chiral carbon atom in citronellal and were able to show the optical isomers appropriately. This response identifies that geraniol has E/Z isomers and provides a correct explanation with reference to the carbon-carbon double bond between carbon atoms 2 and 3. So marking points one and two were given. The candidate recognises that the double bond between carbon atoms 6 and 7 would not cause isomerism in both compounds. Unfortunately this response overlooks the chiral carbon in citronellal and incorrectly states that it has are no stereoisomers. This question highlights the challenge of a linear specification, where content from different modules may be assessed within the same question. Candidates are likely to encounter these two types of stereoisomerism in different years of their course. They should therefore be encouraged to make links between the different modules to help develop their understanding.

Notes from the mark scheme and report

• geraniol: E/Z at C=C of carbon-2,3 (DO NOT ALLOW C=C at carbon-6,7
• IGNORE cis/trans)
• citronellal: chiral carbon-3 with four different groups, optical isomers drawn as 3D mirror images

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects; M4.3 Understand the symmetry of 2-D and 3-D shapes

Mark scheme

Examiner's comment

This question required candidates to use both pieces of information to deduce that B was a carboxylic acid with two equivalent carbon atoms. Many candidates were able to suggest a suitable structure. However some candidates did not use all the information and it was common to see responses that showed an ester or a straight chain carboxylic acid.

Notes from the mark scheme and report

• bromo-substituted C5 carboxylic acid with 4 carbon environments

Mark scheme

Examiner's comment

In this question, candidates were given the opportunity to demonstrate some knowledge of organic reaction in a new context. The choice of reaction was up to the candidate. Most candidates were able to identify the alkene group in terpineol and to suggest a reagent that would react with this functional group. A correct structure for the organic product then usually followed. Although most candidates identified the alcohol group, many struggled with a reagent and resulting product. Although the alcohol –OH group has many reactions, (e.g. elimination, substitution, esterification) many candidates were fixated on oxidation with acidified dichromate despite a tertiary alcohol not being capable of oxidation with this reagent. Some candidates quoted acidified dichromate but then copied the structure of terpineol, stating that there was no reaction, despite the question directing them to select a reagent that would react with their chosen group.

Notes from the mark scheme and report

• functional group MUST be named (alkene
• tertiary alcohol)
• DO NOT ALLOW UV with halogens
• DO NOT ALLOW Cr2O72–/H+ (tertiary alcohol)
• ALLOW addition of HBr/H2O either way across C=C
• reagent must react with that group only

Mark scheme

Examiner's comment

Candidates were required to combine two thiosulfate ions into a feasible dimer. Many acceptable shapes were allowed with different combinations of O and S atoms and several rings. A significant number of candidates did not seem to know where to start and less than half the candidates were able to draw an acceptable structure.

Notes from the mark scheme and report

• must be 2 atoms in the centre between the 6-bonded S atoms (S–S, O–O or S–O link)
• IGNORE charges
• ALLOW cyclic structures

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects

Mark scheme

Examiner's comment

Most candidates attempted a dot-and-cross diagram of a COCl2 molecule, with ionic representations being rare. Candidates should take care to include any lone pairs in their diagrams. Omission of the O and Cl lone pairs was the most common error.

Notes from the mark scheme and report

• lone pairs on Cl (3 LPs) and O (2 LPs) must be included
• O and Cl electrons must be shown differently from C electrons
• IGNORE inner shells

Mark scheme

Examiner's comment

Most candidates that obtained a sensible value for the previous question managed to draw a creditable structure. Allowing error carried forward meant that feasibly derived structures could be credited a mark.

Notes from the mark scheme and report

• structure must match Mr from (d)(i) within 10
• ALLOW ECF only if 2 × COOH possible
• ALLOW incorrect connectivity e.g. –HO

Mark scheme

Examiner's comment

Many candidates correctly identified the two alkenes formed as 2-methylbut-2-ene and 3-methybut-1- ene. Stronger responses used skeletal formula to show the structures clearly. Some candidates preferred to use chemical symbols to represent the atoms present and although this approach is valid, lower ability responses did not show sufficient detail as demonstrated in Exemplar 1. In this response the alkene 2-methylbut-2-ene has been correctly identified and one mark credited. However, the attempt to show 3-methylbut-1-ene does not score. This is because C3H7 has been used instead of CH(CH3)2. Candidates should be encouraged to show every carbon atom when drawing a structure as the use of ambiguous formulae is not sufficient to gain credit.

Notes from the mark scheme and report

• one mark per alkene: 2-methylbut-2-ene and 3-methylbut-1-ene
• either order

Mark scheme

Examiner's comment

Candidates were well prepared to tackle this question and consequently most candidates scored both marks.

Notes from the mark scheme and report

• each structure needs four bonds to the chiral C with at least two wedges
• structures must be mirror images with correct connectivity
• 1 mark max if CH2SH shown as R

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects; M4.3 Understand the symmetry of 2-D and 3-D shapes

Mark scheme

Examiner's comment

In contrast to part (a) this question proved difficult and discriminated well. The higher ability candidates correctly identified the dichloride salt produced by the reaction of lysine with excess acid. Some candidates formed ammonium ions on both nitrogen atoms but omitted the chloride ions. Others only formed a monochloride salt, leaving the R group unchanged. These two approaches scored one mark.

Notes from the mark scheme and report

• BOTH amine groups protonated (excess HCl)
• Cl– required because question asks for salt
• 1 mark if only one NH2 protonated or no Cl–

Mark scheme

Examiner's comment

This question required candidates to apply their knowledge of amide hydrolysis to a section of protein. Many candidates correctly recognised that two amino acids would be produced but not all took account of the alkaline conditions and showed COOH groups rather than carboxylates. Candidates found this question difficult and although many gained some credit only the highest ability candidates, who recognised the amide in the side-chain would also react, scored full marks after. Exemplar 3 shows a good response. This response has correctly identified the amino acid on the left hand side of the amide link and also shown this as a carboxylate. Consequently the first mark has been achieved. The right hand amino acid has also been identified correctly. However, the amide in the R group has not been hydrolysed so this response only scores one of the two marks available for this product. Notice the candidate has presented their structures clearly with the atoms drawn in a similar arrangement to the protein shown in the question. This is a good strategy to avoid errors and omissions when drawing organic structures.

Notes from the mark scheme and report

• one mark per group hydrolysed (side-chain amide also hydrolysed)
• carboxylate –COO–/–COONa required (DO NOT ALLOW COOH)
• DO NOT ALLOW –COO–Na covalent bond
• DO NOT ALLOW sodium salt of the alcohol group
• IGNORE NH3

Mark scheme

Examiner's comment

This question proved difficult and although the majority of candidates scored in some parts, only the very best responses secured all five marks. More detailed feedback is discussed with Exemplar 8. Cinnamaldehyde was the starting point for this flowchart of reactions. The most frequently scored mark was correct identification of the reagents required for the formation of the hydroxynitrile. This response uses NaCN/H+. Other candidates used HCN which was also acceptable. The flowchart shows two different reactions of this hydroxynitrile. The first is the reaction with excess hydrogen in the presence of Ni. Most candidates scored one mark for their product. As in this exemplar, the double bond was often reacted to form a saturated chain. Some candidates identified that the CN group would also react but instead of writing CH2NH2 they replaced the CN group with just NH2, effectivity removing a carbon atom from the chain. The second reaction of the hydroxynitrile is acid hydrolysis of the CN group. This response identifies the correct carboxylic acid. However, this reaction seemed unfamiliar to many candidates and a range of incorrect responses were frequently seen. The final reaction is the reduction of cinnamaldehyde with NaBH4. Many candidates recognised this reaction, but as can be seen in this response the alcohol group is shown on the incorrect carbon atom. This was a common error. Candidates are advised to number carbon atoms present if provided with a complex structure, such as cinnamaldehyde. Numbering will ensure that each carbon is considered when drawing reaction products and would minimise errors, such as those demonstrated in the reduction product.

Notes from the mark scheme and report

• NaCN/H+ or HCN for reagent
• NaBH4 reduces CHO only (C=C unchanged)
• excess H2/Ni reduces both C=C and C≡N (1 mark each
• IGNORE hydrogenation of benzene ring)
• H+(aq) hydrolyses nitrile to COOH

Mark scheme

Examiner's comment

Compound H was also the focus for this question. Most candidates were able to provide the structure of the acyl chloride obtained from H but only some identified SOCl2 as the correct reagent. Common incorrect reagents included HCl and AlCl3. Most candidates recognised that polymer I was a polyester but only some were able to draw two repeat units correctly. Candidates are advised to practice drawing different polymers, taking care to ensure the correct number of repeat units are present when a specific number is required.

Notes from the mark scheme and report

• SOCl2 (ALLOW PCl5 or PCl3)
• acyl chloride with phenol OH kept
• two repeat units with ester link and end bonds shown
• DO NOT ALLOW more than two repeat units
• 1 mark for one correct repeat unit

Mark scheme

Examiner's comment

Most candidates were able to draw clear octahedral 3D shapes of the optical isomers, with good use made of wedges. The best candidates showed an overall 3– charge on each isomer but lower ability candidates did not always cancel down the charges in the Fe3+ and (COO–)2 ions, showing a 3+ charge instead of the overall charge of 3–. (See Exemplar 5)

Notes from the mark scheme and report

• overall 3– charge shown outside brackets
• one mark per isomer
• bonds must go to O atoms of each ligand
• 3D wedges required
• simplified loops for ligands NOT allowed

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects; M4.3 Understand the symmetry of 2-D and 3-D shapes

Mark scheme

Examiner's comment

This part discriminated extremely well with many candidates finding it difficult to convert the bracketed structural formula into a skeletal formula. Common errors were drawing of the mono-ester or omitting a carbon atom in the centre of the structure. Even when incorrect, most attempted answers were skeletal formulae.

Notes from the mark scheme and report

• skeletal diethyl butanedioate
• IGNORE displayed formulae

Mark scheme

Examiner's comment

This part was one of the most challenging on the paper. Candidates needed to link the earlier information for combining two ethanal molecules to derive the product for combining two propanone molecules. Despite the challenge, the highest ability candidates were able to come up with the correct structure.

Notes from the mark scheme and report

• (CH3)2C(OH)CH2COCH3
• connectivity not assessed

Mark scheme

Notes from the mark scheme and report

• C=O 1630–1820 and O–H 3200–3600 must be linked to the bond
• neutral so not a carboxylic acid: hydroxy-aldehyde/ketone isomers
• penalise incorrect connectivity once only

Skills: M3.1 Translate information between graphical, numerical and algebraic forms

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Notes from the mark scheme and report

• dot must be on C-2
• ALLOW –OH

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Notes from the mark scheme and report

• two or more Cl on the alkyl chain with at least one at C-2
• DO NOT ALLOW molecular formula C3H4Cl2O2

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Notes from the mark scheme and report

• E = cyclohexanol
• acid catalyst (H3PO4/H2SO4/H+) AND heat
• DO NOT ALLOW other named acids
• IGNORE water/steam

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Notes from the mark scheme and report

• both points must be comparisons
• fewer points of contact so weaker London forces needing less energy to break
• IGNORE van der Waals
• IGNORE 'less energy to break the bonds'

Mark scheme

Notes from the mark scheme and report

• 1 mark if both shown but in the wrong columns
• DO NOT ALLOW incorrect connectivity e.g. –CH3CH2

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects

Mark scheme

Notes from the mark scheme and report

• 2-bromo-2-methylpentane and 3-bromo-2-methylpentane in either order

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Notes from the mark scheme and report

• NH2 is 2,4-directing (ALLOW ortho/para)
• 2-bromo- and 4-bromophenylamine
• IGNORE electron donating/withdrawing

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Notes from the mark scheme and report

• H2N(CH2)6NH2 and HOOC(CH2)4COOH
• ALLOW diacyl chloride

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Notes from the mark scheme and report

• structure must include OH as part of the COOOH group (C(=O)–O–O–H)

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Notes from the mark scheme and report

• n(NaOH) = 1.89 × 10–3
• ×10 for 250 cm3
• M(A) = 132 so R = C4H9 (57)
• R must be CH(CH3)CH2CH3 to give a second chiral centre
• common error: 25.00 used instead of 22.50 (4 max)
• ALLOW ECF from mean titre

Skills: M0.2 Use ratios, fractions and percentages; M2.3 Substitute numerical values into algebraic equations using appropriate units for physical quantities; M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects; PAG2 Acid–base titration

Mark scheme

Notes from the mark scheme and report

• 2HOCH(R)COOH + Mg → (HOCH(R)COO)2Mg + H2
• redox
• IGNORE poor connectivity to OH groups

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Notes from the mark scheme and report

• pyridine-2-carboxylate with negative charge on O–
• ALLOW brackets with charge outside

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Notes from the mark scheme and report

• skeletal formula required
• IGNORE displayed formula in a second structure

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Notes from the mark scheme and report

• C is the tertiary alcohol
• DO NOT ALLOW more than one repeat unit
• side links required
• DO NOT ALLOW OH– connectivity

Mark scheme

Notes from the mark scheme and report

• DO NOT ALLOW H2O for stage 2
• MAX 2 for a monobrominated intermediate via HBr
• ALLOW dichloro/diiodo compound

Mark scheme

Notes from the mark scheme and report

• mark independently
• DO NOT ALLOW –CH3CH2 connectivity
• DO NOT ALLOW trans-pent-2-ene

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects