Q6(h). Four C₁₀H₁₄ isomers: the one marked by a McLafferty peak
An organic compound with molecular formula C₁₀H₁₄ can exist in four isomeric forms given below. The isomer that can be identified uniquely by mass spectrometry is which one. Explain your answer. [structures of the four isomers 1–4 given in the paper]
Answer in brief
Isomer 2, butylbenzene: only it has a γ-hydrogen, so only it gives the McLafferty ion at m/z 92 beside m/z 91.
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Coversmass spectrometryMcLafferty rearrangementbutylbenzenetropylium ionbenzylic cleavage
All parts of Question 6
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- 6(b) HBr and a conjugated diene: 1,2- and 1,4-addition4 marks
- 6(c) Phenylglycine and mandelic acid from benzaldehyde4 marks
- 6(d) Coumarin and 3-acetylcoumarin from salicylaldehyde4 marks
- 6(e) Intramolecular oxymercuration–demercuration: a cyclic ether4 marks
- 6(f) trans- and cis-Cyclohexane-1,2-diol from cyclohexanone4 marks
- 6(g) [1,5]-Carbon shift and Cope rearrangement4 marks
- 6(h) Four C₁₀H₁₄ isomers: the one marked by a McLafferty peak4 marks
- 6(i) C₃H₇NO with two N–methyl singlets: N,N-dimethylformamide4 marks
- 6(j) ν(C=C) of methylidenecycloalkanes and ring size4 marks