Edexcel Jan 2017 (IAL) Paper 5 Q23

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A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D 23 Amino acids contain both amine and carboxylic acid functional groups. (a) The amino acid alanine can be synthesised from ammonia and ethanal in three steps. CH3 NH3 Step 1 HN H2O CH3 Step 2 H2N OH CH3 alanine Step 3 H2N C CH3 (i) Suggest the reagent for Step 2. (1)(ii) Identify, by name or formula, the reagent for Step 3. (1)(iii) Use your knowledge of amine chemistry to suggest the displayed formula of the organic product formed when alanine reacts with chloroethane. (1) A E R A S I H T N I E T I R W T O N O D *P48373A01732* 17 Turn over<br /> (b) Tyrosine and serine are amino acids that contain an additional OH group. H2N CH2 OH H2N OH CH2 OH OH tyrosine serine (i) Draw the structure of the zwitterion of tyrosine. 18 *P48373A01832* D O N O T W R I T E I N T H I S A R E A (1) D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> (ii) Complete the diagrams to show the two optical isomers of serine. (2) H2N OH CH2 OH - - - - - - - - - - C A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P48373A01932* 19 Turn over<br /> (iii) Tyrosine and serine can form different types of condensation polymers. Draw two repeat units of the polyamide formed from tyrosine only and two repeat units of the polyester formed from serine only. The polymer linkages must be displayed. (4) H2N CH2 OH H2N OH CH2 OH OH tyrosine serine Polyamide formed from tyrosine only 20 *P48373A02032* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> Polyester formed from serine only A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P48373A02132* 21 Turn over<br /> (c) Amino acids are detected using ninhydrin. OH OH ninhydrin Ninhydrin reacts with most amino acids to give a purple colour. The reaction can be summarised as D O N O T W R I T E I N T H I S A R E A + NH2CHCOOH OH OH + RCHO + CO2 + 3H2O (i) Draw the structure of the aldehyde formed when tyrosine reacts with ninhydrin. (1) H2N CH2 OH tyrosine OH D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A 22 *P48373A02232*<br /> (ii) Draw the structure of the amino acid that reacts with ninhydrin to form 2-methylpropanal, (CH3)2CHCHO. A E R A S I H T N I E T I R W T O N O D (d) Explain whether or not tyrosine and serine can be distinguished by their infrared absorbance in the 4000 to 2000 cm1 range. Justify your answer by quoting information from the Data Booklet. (1) (1) A E R A S I H T N I E T I R W T O N O DA E R A S I H T N I E T I R W T O N O D *P48373A02332* 23 Turn over<br /> (e) This question is about the high resolution proton nmr spectrum of the amino acid valine. H3C CH3 NH2 OH (i) State the total number of different proton environments in valine. (1) D O N O T W R I T E I N T H I S A R E A(ii) Use the Data Booklet, and your knowledge of nmr spectra, to complete the table for the protons in valine shown in bold in the structure. Protons in valine Chemical shift / ppm from TMS Splitting pattern (3) CH3 CH OH 0.11.9 0.11.9 singlet (Total for Question 23 = 17 marks) TOTAL FOR SECTION B = 47 MARKS 24 *P48373A02432* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D BLANK PAGE A E R A S I H T N I E T I R W T O N O D *P48373A02532* 25 Turn over<br />

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