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CAIE A-Level Chemistry 22.2.5 Carbon Atoms from the M+1 Peak

Practise calculating carbon count from relative M and M+1 abundances using the 1.1% carbon-13 contribution.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • substitute both relative peak abundances into n = 100 × [M+1] / (1.1 × M)
  • keep M and M+1 peak intensities in the same abundance scale before calculating
  • rearrange the same relationship to predict the M+1 abundance when carbon count and M are given

22.2.5—The number of carbon atoms, n, in a compound question 1

[Maximum number: 1]

Fig. 4.1 shows how propane, C3H8\mathrm{C}_{3} \mathrm{H}_{8}, can be converted to propanoic acid, CH3CH2COOH\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}.

Fig. 4.1

Fig. 4.1

CH3CH2COOH\quad \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH} reacts with an unsaturated alcohol R to form unsaturated ester S.

The mass spectrum of S shows the following peaks.

Table 4.3

Table 4.3

Use Table 4.3 to calculate the number of carbon atoms in S.
number of carbon atoms in S=

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