Q8(c)(ii). Two isomeric amides C₅H₁₁NO by mass spectrometry
How could the above pair of isomeric compounds be differentiated by mass spectrometry? [structures of (I) and (II), isomeric amides C₅H₁₁NO, given in the paper]
Answer in brief
Only (II) has a γ-hydrogen, so only (II) gives the McLafferty ion at m/z 73 (M − 28, loss of ethene); (I) shows α-cleavage ions at m/z 72 and 57 instead.
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CoversMcLafferty rearrangementmass spectrometryγ-hydrogenα-cleavageamide fragmentation
All parts of Question 8
- 8(a)(i) Doxepin: site of ionisation, m/z 58 ion and metastable ion10 marks
- 8(a)(ii) Ketone C₇H₁₂O with λmax = 249 nm5 marks
- 8(b)(i) Microwave activity; rotational constants of CO10 marks
- 8(b)(ii) Expected J(Ha–Hb) in three alkenes5 marks
- 8(c)(i) Keto and enol percentages of acetylacetone from integration10 marks
- 8(c)(ii) Two isomeric amides C₅H₁₁NO by mass spectrometry5 marks
- 8(c)(iii) Fundamental vibrations of CO₂ and their IR activity5 marks