Proton NMREdexcel A-Level Chemistry: Mind map

Exam questions on Proton NMR

1. A student records the high-resolution 1H NMR spectrum of bromoethane, CH₃CH₂Br.
   Explain why the peak caused by the CH₃ protons is a triplet.2 marks
2. A chemist records the high-resolution 1H NMR spectrum of ethanal, CH₃CHO. It shows two peaks, at chemical shifts (δ) of 2.2 ppm and 9.8 ppm.
   Explain the splitting patterns of the two peaks in the spectrum of ethanal.2 marks
3. A chemist has an unlabelled ester which is either ethyl ethanoate, CH₃COOCH₂CH₃, or methyl propanoate, CH₃CH₂COOCH₃. Its high-resolution 1H NMR spectrum has three peaks: δ 1.2 (triplet, relative area 3), δ 2.0 (singlet, relative area 3) and δ 4.1 (quartet, relative area 2). Typical shift ranges (ppm): CH₃ in an alkyl chain 0.7–1.3; CH₃ or CH₂ next to C=O 2.0–2.7; CH₃ or CH₂ bonded to the oxygen of an ester 3.6–4.3.
   Explain how the relative areas and the splitting patterns show that the ester contains a CH₃CH₂ group.3 marks