A-LevelChemistryIntroduction to organic chemistry9701/43 · Oct/Nov 2022 · Q717 Marks

The structure of compound P is shown in Fig. 7.1. P H2N / C-CH2- / C=O O-CH3 Benzene ring attached to -CH2- [Figure 7.1]

(a)(i)P is optically active. Use an asterisk (*) to identify all chiral carbon atoms on the structure of P in Fig. 7.1.[1]
(a)(ii)Plane polarised light is passed through a pure sample of one enantiomer of P. This is then repeated with a pure sample of the other enantiomer of P. Describe the results of these two experiments, stating the similarities and differences of the results.[2]
(b)(i)P can be used to make compound Q in a single step reaction. [Structure of Q: Benzene ring -CH₂-CH(NH-C(=O)CH₃)-COOCH₃] Give the structural formula of the compound that is added to P to make Q and give the formula of the other product of this reaction. compound added to P other product[1]
(b)(ii)When an ester is treated with LiAlH₄ in dry ether the ester linkage is cleaved by the addition of four hydrogen atoms and two alcohols are produced. Draw the structures of the compounds formed when Q is treated with an excess of LiAlH₄ in dry ether.[3]
(b)(iii)Compare the relative basicities of compound P, compound Q and phenylamine. least basic < most basic Explain your answer.[3]
(c)(i)P can be used to make compound R in a two-step reaction, shown in Fig. 7.2. [Figure 7.2 showing P to R, where R is H₂N-C₆H₄-CH₂-CH(NH₂)-COOH with the ring NH₂ para to the side chain] Identify the reagents and conditions used for the two steps of the reaction. step 1 step 2[2]
(c)(ii)Complete Table 7.1 by drawing the structures of the organic products formed when R is treated separately with the reagents given. [Table 7.1 with HNO₂(aq) at 4°C and excess Br₂(aq) at room temperature as reagents][2]
(d)(i)P can be used to produce compound T. [Structure of T: Benzene ring -CH₂-CH(NH₂)-COOH] In aqueous solution, T has a property called an isoelectric point. Explain what is meant by isoelectric point.[1]
(d)(ii)T can polymerise under suitable conditions. No other monomer is involved in this reaction. Draw a section of the polymer chain formed that includes three T monomers. Identify the repeat unit on your diagram.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

[1] * on chiral carbon atom (which has -H, -NH2, -CH2-Ph, -COOCH3) [1]
[2] plane of polarised light will be rotated (in both isomers) [1] by same angle / equal amounts in opposite directions [1]
[1] CH3COCl AND HCl
[3] HN(CH2Ph)CH2OH [1] and CH3OH [1] (alcohol from ester) and correct structure for reduction of amide (CH3CONH- to CH3CH2NH-) [1]
[3] Q < phenylamine < P [1] any three from: ability of N to accept a proton OR donate its lone pair to a proton phenylamine lone pair of N delocalised into ring OR p-orbital on N overlaps with π cloud of ring (and decreases electron density on N) compound P (2° amine) alkyl group has a positive inductive effect (and increases electron density on N) compound Q (amide) lone pair of N (in amide) delocalised by C=O OR overlap of lone pair of N with C=O (and decreases electron density on N)
[2] conc. HNO₃ and H₂SO₄ (25 °C < T ≤ 60 °C) [1] Sn and conc. HCl and reflux (followed by NaOH(aq)) [1]
[2] NH₂ on ring gives diazonium ion [1] dibromo compound with Br atoms 2,6 to amine group [1]
[1] pH where the species is a zwitterion is the dominant form OR pH where the species is electrically neutral
[2] repeat unit identified by label / brackets / circle [1] three monomers complete all amide/peptide bonds correct all CHCH₂C₆H₅ / CHR groups correct trailing bonds or other convention(everything else correct) [1]