OCR A Jan 2013 Paper 4 Q3

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3 Penicillamine is an -amino acid that is used as a drug to treat rheumatoid arthritis. 10 The structure of penicillamine is shown below. CH3 H3C SH NH2 OH penicillamine (a) Explain why penicillamine is described as an -amino acid.[1] (b) Penicillamine exists as a zwitterion in aqueous solution. (i) Draw the structure of this zwitterion. (ii) Dilute aqueous acid is added to an aqueous solution of penicillamine. Draw the structure of the ion that forms. [1] [1]OCR 2013<br />
 11 (c) Penicillamine exists as optical isomers. Only one isomer is pharmacologically active. Its 3-D structure is shown below. In the box below, draw a 3-D diagram to show the structure of the other optical isomer of penicillamine. C(CH3)2SH H2N COOH pharmacologically active isomer of penicillamine (d) The SH (thiol) group shows similar chemical properties to OH. (i) The SH and NH2 groups in penicillamine react with halogenoalkanes by nucleophilic substitution. Penicillamine reacts with a dihalogenoalkane to form the compound shown below. [1] CH3 H3C NH OH HH Suggest the formula of a dihalogenoalkane that will react with penicillamine to form this compound.[1]OCR 2013 Turn over<br />
 (ii) Penicillamine is able to undergo condensation polymerisation to form polypeptide chains. Draw two repeat units of a polypeptide chain of penicillamine. 12 [2] (e) Penicillamine is a structural isomer of methionine, which is also an -amino acid. CH3 H3C SH NH2 OH penicillamine H3C NH2 OH methionine NMR spectroscopy can be used to distinguish samples of the two isomers. (i) Predict the number of peaks in the 13C NMR spectrum of each of these -amino acids. penicillaminemethionine[2]OCR 2013<br />
 (ii) A 1H NMR spectrum of penicillamine showed five peaks. 13 A solution of penicillamine was shaken with a few drops of D2O and a second 1H NMR spectrum was run. The second 1H NMR spectrum is shown below. 12 10 (cid:303) / ppm Identify the three types of protons in penicillamine responsible for the peaks that disappeared in the second 1H NMR spectrum. Explain why these peaks were not seen in the second spectrum.[2]OCR 2013 Turn over<br />
 14 (iii) 1H NMR spectroscopy can be used to distinguish between penicillamine and methionine. Complete the table below to predict the 1H NMR spectrum of methionine, which is shown below. The actual chemical shifts for three types of proton in methionine have been added for you. H3C NH2 OH methionine 1H NMR spectrum for methionine Type of proton(s) Chemical shift,/ppm Splitting pattern Relative peak area NH2 H3CS SCH2 4.5 2.1 2.4 Singlet [5] [Total: 16]OCR 2013<br />

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