18 Which splitting patterns will be shown by the signals due to the protons marked a, b and c in the 'H NMR spectrum of ibuprofen? H3C CH3 H2C H a 4c-c-cooh bH ibuprofen A. O a = doublet, b = quartet, c = singlet B. O a = triplet, b = doublet, c = doublet C.O a = triplet, b = singlet, c = singlet D. O a = doublet, b = quartet, c = doublet a is split by the single proton on the adjacent carbon atom into a doublet. b is split by the three protons on the adjacent carbon atom into a quartet. As there are no protons on the carbon atom adjacent to the acidic proton, c is not split. 19 Which will show a single signal with no splitting pattern (i.e. a singlet) in their high resolution 'H NMR spectrum? 1. benzene II. 2,2-dimethylpropane III. 2-methylpropane A. O I, II and III B. I and III only o I and II only D. O II and III only In both benzene, C6H6 and 2,2-dimethylpropane, C(CH3)4 all the hydrogen atoms in the molecule are in an identical chemical environment. In 2-methylpropane the single proton will be split by the protons in the three methyl groups and the signal from the methyl protons will be split into a doublet by the single proton. 20 Which information from their 'H NMR spectra could be used to distinguish between methyl propanoate and ethyl ethanoate? A. O the number of signals B. O the chemical shift of each absorption C. O the ratio of the areas under the signals D. O the splitting patterns Methyl propanoate, CH3CH2COOCH3 and ethyl ethanoate, CH3COOCH2CH3 will both give three signals as the hydrogen atoms are in three separate environments. Both will have the same ratio of 3:3:2 and both will show a singlet (from the isolated -methyl group), a triplet and a quartet (due to the ethyl group). The only difference will be in the chemical shift