13 - A-level chemistry (AQA and OCR)

13.11 EXERCISE 1 – Mass spectra

1.

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b)

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3.

State the species responsible for the four other peaks in the mass spectrum of butanal and write equations to show their formation from the molecular ion. Suggest which one of these peaks will not be present in a mass spectrum of methylpropanal, giving a reason for your choice. Butanal and methylpropanal give slightly different mass spectra. Both give a molecular ion peak at m/z = 72, but butanal gives four other peaks whereas methylpropanal only gives three. Suggest how pentan-2-one and pentan-3-one could be distinguished in a mass spectrum. Write equations to show the formation of any important fragment ions. Write equations to show the formation of at least two species giving intense peaks in the mass spectra of each of the following molecules: a) pentane b) ethyl ethanoate c) propanoic acid d) pentanal