Principles of NMR and carbon-13 NMRAQA A-Level Chemistry: Mind map

Exam questions on Principles of NMR and carbon-13 NMR

1. Nuclear magnetic resonance (NMR) spectroscopy is used together with other analytical techniques to confirm the structures of new compounds. A chemist records ¹³C NMR spectra of samples dissolved in a suitable solvent, with tetramethylsilane (TMS), Si(CH₃)₄, added as a standard.
   Explain what is meant by chemical shift and why the chemical shift of a carbon atom depends on its molecular environment.2 marks
2. Compound Y has the molecular formula C₄H₈O₂. Its ¹³C NMR spectrum has four peaks, at δ = 14, 21, 60 and 171 ppm. Data booklet shift ranges (δ / ppm): C–C 5–40; C–O 50–90; C=C 90–150; C=O (esters, carboxylic acids) 160–185; C=O (aldehydes, ketones) 190–220.
   State the type of carbon atom responsible for the peak at δ = 171 ppm and for the peak at δ = 14 ppm in the spectrum of Y, using the shift ranges given.2 marks
3. Compound Z has the molecular formula C₃H₆O. Its ¹³C NMR spectrum has two peaks, at δ = 30 and δ = 206 ppm. Data booklet shift ranges (δ / ppm): C–C 5–40; C–O 50–90; C=C 90–150; C=O (esters, carboxylic acids) 160–185; C=O (aldehydes, ketones) 190–220.
   Deduce the structure of Z. Explain your reasoning using the spectrum.3 marks