CIE Jun 2016 v2 Paper 4 Q6

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Esterases are enzymes that hydrolyse esters. 12 + H2O + HOR' O R' O H PMT Enzymes can be quite specific in the structures of the substrates they act upon. For example, an esterase isolated from the mould Aspergillus niger will hydrolyse phenyl ethanoate, CH3CO2C6H5, but not its isomer methyl benzoate, C6H5CO2CH3. (a) Outline how enzymes catalyse reactions, and explain their specificity. Use diagrams in your answer where appropriate.[3]UCLES 2016 9701/42/M/J/16<br /> 13 (b) Sample bottles of each of the isomers phenyl ethanoate and methyl benzoate have lost their labels and so have been named isomer A and isomer B. (i) The carbon-13 NMR spectra of isomers A and B contain the following peaks. PMT isomer A52128129130133167 isomer B26122126129151169 The identity of the compound responsible for each spectrum can be deduced by studying the chemical shifts () of the peaks in the spectra. Use the Data Booklet to assign the correct peaks to the labelled carbon atoms in the structures of the isomers below. Write each value next to the relevant carbon atom and hence deduce the identity of each isomer.CH3C O O CCH3phenyl ethanoate is isomermethyl benzoate is isomer[2] (ii) These two isomers are difficult to distinguish chemically. Describe a method of converting them to suitable products in step 1 which can then be tested in step 2. You should state the reagents and conditions for each step, and any observations you would make. step 1step 2[3]UCLES 2016 9701/42/M/J/16 [Total: 8] [Turn over<br />

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