Carbon-13 NMREdexcel A-Level Chemistry: Mind map

Exam questions on Carbon-13 NMR

1. A technician in a teaching laboratory has two unlabelled bottles of propanol isomers, one containing propan-1-ol and the other propan-2-ol. Both have the molecular formula C₃H₈O. She plans to tell them apart by recording the 13C NMR spectrum of each.
   Propan-2-ol, CH₃CH(OH)CH₃, gives only two peaks in its 13C NMR spectrum. Explain why.2 marks
2. A pharmaceutical chemist records the 13C NMR spectrum of the solvent ethyl ethanoate, CH₃COOCH₂CH₃. It shows four peaks, at chemical shifts (δ) of 14, 21, 60 and 171 ppm.
   Explain why the peak at δ 171 ppm is at a much higher chemical shift than the peak at δ 14 ppm.2 marks
3. A laboratory holds four isomeric alcohols of molecular formula C₄H₁₀O: butan-1-ol, butan-2-ol, 2-methylpropan-1-ol and 2-methylpropan-2-ol. A technician uses 13C NMR spectroscopy to tell them apart. Typical chemical shift ranges (ppm): C–C 5–40; C–O 50–90.
   Deduce the number of peaks in the 13C NMR spectra of 2-methylpropan-2-ol and of 2-methylpropan-1-ol, and justify your answers.3 marks