OCR A Jan 2011 Paper 4 Q5

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5 Rose oil can be extracted from the flowers, leaves and roots of roses using the apparatus below. 10 flowers, leaves and roots of roses heat coolant rose oil (a) The rose oil contains a mixture of compounds, some of which can be separated by using thin- layer chromatography (TLC). The chromatogram obtained is shown below. solvent front base line Fig. 5.1 (i) Explain how TLC separates compounds in the mixture. In your answer, you should use appropriate technical terms, spelled correctly.[1] (ii) Estimate the Rf value of A. [1]OCR 2011<br /> (iii) Using the chromatogram in Fig. 5.1, suggest why it is not possible to conclude that the rose oil contains only three different compounds. 11[1] (b) GCMS was used to identify the compounds present in the rose oil as nerol, geraniol, citral and menthol, shown below. These compounds all have stereoisomers. nerol OH OH citral OH geraniol menthol (i) Explain how GCMS can be used to identify these compounds in the rose oil.[1] (ii) Suggest, with a reason, which two compounds might be present in B in Fig. 5.1.[1] (iii) Explain what is meant by the term stereoisomers.[1]OCR 2011 Turn over<br /> (iv) Draw a circle around the feature in citral that causes the stereoisomerism. 12 citral [1] (v) Identify with asterisks (*) all stereoisomerism. the chiral centres in menthol that cause the OH menthol [2] (c) Menthol is used in a wide range of products including lip balms, cough medicines and perfumery. The demand for menthol exceeds the supply from natural sources. Menthol is manufactured, using a chiral synthesis, from myrcene, a readily available starting material. OH myrcene menthol Calculate the mass of menthol that can be synthesised from 34.0 g of myrcene. The percentage yield is 60%. Mr (Myrcene) = 136.OCR 2011 mass of menthol =g [3] [Total: 12]<br />

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