Q13-19P - Organic Chemistry (Mcmurry)

Question

Classify the resonances in the ¹³C NMR spectrum of methyl propanoate,${\mathbf{CH}}_3{\mathbf{CH}}_2{\mathbf{CO}}_2{\mathbf{CH}}_3$ .

Step-by-Step Solution

Answer

NMR Spectra

Step 1: 13 C 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.

Step 2: 13 C 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