OCR A Jun 2013 Paper 4 Q5

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5 A chemist isolated compound L from the leaves of a common garden herb. He analysed the compound using a number of techniques. 15 (a) Compound L contains C, H and O only. Elemental analysis shows that L has the percentage composition by mass: C, 73.15%; H, 7.37%. The mass spectrum of L has a molecular ion peak at m/z = 164. Show that the molecular formula of L is C10H12O2. [2]OCR 2013 Turn over<br />
 (b) The 13C NMR spectrum of compound L is shown below. 16 240 220 200 180 160 140 100 80 60 40 20 120 (cid:419)/ppm How many different carbon environments (types of carbon) are present in a molecule of compound L?[1] (c) The 1H NMR spectrum of compound L, C10H12O2, is shown below. One of the signals has been enlarged to help its analysis. expansion of multiplet centred at (cid:419) = 2.7 ppm 1H 6H (cid:419)/ppm 5HOCR 2013<br />
 (i) A signal at (cid:419) = 0 ppm results from tetramethylsilane (TMS). TMS had been added to the sample of compound L before the NMR spectrum was run. 17 State why TMS was added.[1] (ii) The 1H NMR spectrum includes an integration trace. What information can be deduced about compound L from the integration trace?[1] (iii) Using the information given in parts (a), (b) and (c) of this question, determine the structure of compound L. Show all your reasoning. In your answer, you should use appropriate technical terms, spelled correctly. structure of compound LOCR 2013 Turn over<br />
 18[7] [Total: 12] END OF QUESTION PAPEROCR 2013<br />

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