Question

Classify the resonances in the¹³C NMR spectrum of methyl propanoate,${\mathbf{CH}}_3{\mathbf{CH}}_2{\mathbf{CO}}_2{\mathbf{CH}}_3$.

Short answer

NMR Spectra

Step-by-step solution

13C NMR spectroscopy

Most ¹³C resonances are between 0 and 220 ppm downfield from the TMS reference line, with the exact chemical shift of each ¹³C resonance dependent on that carbon’s electronic environment within the molecule.

Generally, the chemical shift is affected by the electronegativity of a nearby atom like oxygen, nitrogen, halogen, etc.

13C NMR spectrum for methyl propanoate

The chemical shift value for the carbonyl carbon of ester is 174.9 ppm. While the ${\text{-CH}}_{\text{3}}$group which is attached to the oxygen has a chemical shift value of 51.5 ppm. Also, the ${\text{-CH}}_{\text{3}}$group which is attached to ${\text{-CH}}_{\text{2}}$group is about 9.2 ppm. The ${\text{-CH}}_{\text{2}}$group which is connected to carbonyl carbon has a chemical shift value of 27.5 ppm.

NMR Spectra