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CIE Jun 2017 v2 Paper 4 Q8
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![(a) The amino acid tyrosine can be synthesised from phenol by the route shown. 18 step 1 HO CHO step 2 HO HO phenol NH2 step 5 CO2H HO Cl CO2H step 4 1. PCl 5 2. H2O HO HO tyrosine PMT OH CN step 3 OH CO2H (i) Name the mechanism occurring in the following steps. step 1step 2[2] (ii) What type of reaction is occurring in step 3?[1] (iii) Suggest reagents and conditions for each of the following steps. step 1step 2step 3step 5[5]UCLES 2017 9701/42/M/J/17<br />
(iv) Draw the structures of the products of the reactions of tyrosine with an excess of each of the following reagents. 19 PMT with NaOH(aq) with HCl (aq) with Br2(aq) [4] Question 8 continues on the next page.UCLES 2017 9701/42/M/J/17 [Turn over<br />
(b) The dipeptide phe-tyr has the following structure. 20 PMT H N CO2H H2N OH A mixture of this dipeptide (phe-tyr) and its two constituent amino acids (phe and tyr) was subjected to electrophoresis in a buffer at pH 12. At the end of the experiment the following results were seen. Spots R and S remained very close together. mixture applied here R S The three spots are due to the three species phe, tyr and phe-tyr. (i) Which species is responsible for spot P? Explain your answer.[2] (ii) Suggest why the other two species give spots R and S that are so close together.[1] [Total: 15] Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge International Examinations Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cie.org.uk after the live examination series. Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.UCLES 2017 9701/42/M/J/17<br />](https://learnah.org/wp-content/uploads/2018/08/June_2017_v2_QP_-_Paper_4_CIE_Chemistry_A-level_8-0.jpg)
![9701/42 Question 7(b)(i) 7(b)(ii) Cambridge International AS/A LevelMark Scheme PUBLISHED Answer CH2COCl or Cl CHO or COCl CH3 CHO CH2Cl HO COCH3 Cl CH=CH2 Cl OR any chiral atom correctly labelled Question 8(a)(i) step 1 electrophilic substitution step 2 nucleophilic addition 8(a)(ii) hydrolysis Answer Total: ignore acylation PMT May/June 2017 Marks 1 + 1 1 + 1 10 Marks 1 1 1UCLES 2017 Page 11 of 13<br />
9701/42 Question 8(a)(iii) step 1 Cl CH2CHO Cambridge International AS/A LevelMark Scheme PUBLISHED Answer 8(a)(iv) Al Cl3 step 2 HCN + NaCN step 3 heat in H3O+ / heat H+(aq) step 5 NH3 under pressure (+ heat) or heat NH3 in a sealed tube with NaOH(aq) NH2 CO2 [2] with HCl(aq) NH3 CO2H [1] HO with Br2(aq) Br HO Br NH3 CO2 or Br HO Br NH2 CO2H [1] 8(b)(i) P is tyr tyr is 2 AND it is small / has a small MrUCLES 2017 Page 12 of 13 PMT May/June 2017 (allow Br, I for Cl ) Marks 1 1 1 1 1 1 + 1 1 1<br />
Cambridge International AS/A LevelMark Scheme PUBLISHED Answer (dipeptide / phe-tyr) 2 is about double the Mr / mass of (phe) 1 OR mass / charge ratios are about the same for each (for dipeptide / phe-tyr and phe) 9701/42 Question 8(b)(ii) PMT May/June 2017 Marks 1 Total: 15UCLES 2017 Page 13 of 13<br />](https://learnah.org/wp-content/uploads/2018/08/June_2017_v2_MS_-_Paper_4_CIE_Chemistry_A-level_8-0.jpg)
