CIE Jun 2015 v2 Paper 4 Q8

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14 (a) NMR spectroscopy and X-ray crystallography can both be used to examine the structure of organic compounds. NMR is very useful at examining hydrogen atoms in compounds, but hydrogen atoms are invisible to X-rays. (i) Explain why NMR spectroscopy can detect hydrogen atoms in molecules.[1] (ii) Explain why hydrogen atoms are invisible to X-rays.[1] (iii) The molecular formula of the amino acid cysteine is C3H7O2NS. Explain which of the atoms present would show the greatest absorption on exposure to X-rays.[1] (b) The NMR spectrum below was obtained from an organic liquid, P, which containsve carbon atoms per molecule. 10 5/ ppm (i) How many protons are present in one molecule of P? Explain your answer. number of protons[1]UCLES 2015 9701/42/M/J/15<br /> 15 (ii) When a little D2O is added to P, the absorption at2.0 disappears. Explain what this tells you about the group responsible for this absorption and why.[2] (iii) What does the absorption at0.9 tell you about the adjacent carbon atom?[1] (iv) What group(s) is/are responsible for the absorption at0.9?[1] (v) Suggest a structure for P. (c) When an isomer of P is heated with concentrated H2SO4 it forms a new compound, Q. This new compound Q reacts with bromine to give a dibromide, R. (i) A mass spectrum was obtained of R. The ratio of the heights of the M : M+1 peaks was 9.3 : 0.5. Show that there areve carbon atoms present in one molecule of R. [1] (ii) Predict the ratio of the heights of the M : M+2 : M+4 peaks as a result of the two bromine atoms in the dibromide R. Show your working. [1] (iii) What is the molecular formula of R?[1] ratio[1]UCLES 2015 9701/42/M/J/15 [Total: 12] [Turn over<br />

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