Question

Assign as many resonances as you can to specific carbon atoms in the ¹³C

NMR spectrum of ethyl benzoate.

Short answer

The number of absorptions in the ¹³C NMR spectra of the compounds is based on the number of non equivalent carbons in the compound. Each different kind of carbon produces a different signal in the ¹³C NMR spectra.

Step-by-step solution

13C NMR spectroscopy

The number of absorptions in the ¹³C NMR spectra of the compounds is based on the number of non equivalent carbons in the compound. Each different kind of carbon produces a different signal in the ¹³C NMR spectra.

Assigning resonance as you can to specific carbon atoms in the 13C NMR spectrum of ethyl benzoate

The degree of unsaturation for this compound can be found as:

The compound has five degrees of unsaturation.

The spectrum shows seven signals whereas the given molecular formula has nine carbon atoms. Hence all the carbon atoms are chemically inequivalent.

The signals at 14 ppm in the region of 166 ppm indicates the sp³hybridized carbon atom which can be methyl/methylene or methine groups.

One signal in the region of 166 ppm indicates the sp³ hybridized carbon atom directly connected to the oxygen atom.

DEPT -90: The spectrum appears a signal at 127 ppm represents a CH group.

DEPT -135: The CH₂gives negative signal. The CH₃ and CH groups give positive signal.

The two positive signals indicate the presence of methyl groups at 14.0 ppm and a methine group at 134 ppm since a signal appears in the DEPT-90 spectrum and is directly connected to the functional group.

A negative signal at 61 ppm indicate the presence of one methylene group. Only methylene groups appear negative in the spectrum.

The above structure has no symmetry and exhibit seven signals in the ¹³C NMR spectrum.

Ethyl benzoate with the delta values at the different carbons