A-LevelChemistryIntroduction to organic chemistry9701/41 · Oct/Nov 2022 · Q717 Marks

The structure of compound P is shown in [Fig. 7.1]. [Figure 7.1 showing structure of compound P: H2N-CH(CH2C6H5)-C(=O)O-CH3] P is optically active. Use an asterisk (*) to identify all chiral carbon atoms on the structure of P in Fig. 7.1. [1]

(a)(i)The structure of compound P is shown in [Fig. 7.1]. [Figure 7.1 showing structure of compound P: H2N-CH(CH2C6H5)-C(=O)O-CH3] P is optically active. Use an asterisk (*) to identify all chiral carbon atoms on the structure of P in Fig. 7.1. [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][2]
(b)(i)P can be used to make compound Q in a single step reaction. [Figure structure of compound Q: H2N-CH(CH2C6H5)-C(=O)NH-CH3] 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][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][3]
(b)(iii)Compare the relative basicities of compound P, compound Q and phenylamine. least basic < most basic Explain your answer. [3][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 reaction P to R, where R is H2N-C6H4-CH(CH2C6H5)-COOH] Identify the reagents and conditions used for the two steps of the reaction. step 1 step 2 [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 reagents HNO2(aq) at 4°C and an excess of Br2(aq) at room temperature, with empty product columns] [2][2]
(d)(i)P can be used to produce compound T. [Figure structure of compound T: H2N-CH(CH2C6H5)-COOH] In aqueous solution, T has a property called an isoelectric point. Explain what is meant by isoelectric point. [1][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][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 the carbon atom bonded to H2N, H, CH2C6H5 and COO-CH3 (the alpha carbon in H2N-CH(R)-COO-CH3)
[2] plane of polarised light will be rotated (in both isomers) [1] by same angle / equal amounts in opposite directions [1]
[1] compound added to P: CH3NH2 other product: HCl
[3] H2N-CH(CH2C6H5)-CH2OH and CH3OH (structures as shown in the mark scheme)
[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] step 1: conc. HNO3 and H2SO4 (25 °C < T ≤ 60 °C) [1] step 2: Sn and conc. HCl and reflux (followed by NaOH(aq)) [1]
[2] Product with HNO2(aq) at 4°C: Diazonium ion structure (as shown in the mark scheme) Product with an excess of Br2(aq) at room temperature: Dibromo compound structure with Br atoms 2,6 to amine group (as shown in the mark scheme)
[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]