Proton NMRAQA A-Level Chemistry: Mind map

Exam questions on Proton NMR

1. A chemist records ¹H NMR spectra of organic compounds to find how many hydrogen atoms are in each environment. The sample for each spectrum is dissolved in a solvent, and tetramethylsilane (TMS) is added as the standard.
   The integration values for the three peaks in the spectrum of an ester, C₄H₈O₂, are 6.0, 4.0 and 6.0 (arbitrary units). Explain how these data are used to work out the relative numbers of equivalent protons.2 marks
2. The ¹H NMR spectra of aliphatic compounds show splitting of peaks by hydrogen atoms on adjacent carbon atoms. A student is predicting the splitting patterns for 1,1-dichloroethane, CH₃CHCl₂, using the n + 1 rule.
   Use the n + 1 rule to explain why the signal from the CH₃ protons in 1,1-dichloroethane is split in the way you chose in part (a).2 marks
3. Compound R has the molecular formula C₄H₈O₂. Its ¹H NMR spectrum has three peaks: δ = 1.2 (triplet, relative area 3), δ = 2.1 (singlet, relative area 3) and δ = 4.1 (quartet, relative area 2). Shift data (δ / ppm): R–CH₃ 0.7–1.2; CH₃ next to C=O 2.1–2.6; CH₂ bonded to the O of an ester 3.7–4.1.
   Explain how the splitting patterns in the spectrum of R show that it contains an ethyl group, –CH₂CH₃, attached to an atom with no hydrogen atoms.3 marks