OCR A Jun 2010 Paper 4 Q4

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Two esters, CH3(CH2)2COO(CH2)3CH3 and CH3(CH2)2COOCH2CH3, contribute to the odour of pineapple. A food scientist analysed a sample of pineapple essence by separating the two esters using gas chromatography, GC, and measuring their retention times. 10 (a) (i) State what is meant by retention time.[1] (ii) Explain the possible limitations of GC in separating the two esters.[1] (iii) Give the systematic name for the ester CH3(CH2)2COO(CH2)3CH3.[1] (b) The unsaturated ester, ethyl deca-2,4-dienoate contributes to the flavour of pears. (i) Draw the structure of this ester. (ii) When pears ripen, ethyl deca-2,4-dienoate is formed following the breakdown of triglycerides. Draw the general structure of a triglyceride with any functional groups fully displayed. You can use R to represent the carbon chains. [2]OCR 2010 [1]<br />
 (c) The food scientist decided to synthesise the ester shown below, for possible use as a flavouring. 11 CH2 CH2 CH2 The only organic compound available to the food scientist was phenylethanal (C6H5CH2CHO). Explain how the food scientist was able to synthesise this ester using only phenylethanal and standard laboratory reagents. In your answer, you should use appropriate technical terms, spelt correctly. (cid:4)[7]OCR 2010 [Total: 13] Turn over<br />

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