Question

Question: How would the compounds in each pair differ in their IR spectra?

a.

b.

c.

d.

Short answer

Answer

1. The carbonyl absorption peak of amide will be present at a lower wavenumber.
2. The five-membered ester will show CO absorption at a higher wavenumber.
3. The secondary amide(-CONHR: one N-H ) shows one absorption peak, while the primary amide shows two absorption peaks(-CONH₂: two N-H bands)
4. The anhydride will show two CO absorption peaks.

Step-by-step solution

Step-by-Step SolutionStep 1: IR spectrum

The plot of percent transmittance vs. wavelength obtained by the interaction of a compound with Infra-red radiations is termed an IR spectrum.

Each group present in a compound shows a characteristic absorption peak in the IR spectrum.

Difference in IR spectrum of the compounds

a. The given compounds are an ester and an amide.

The compounds can be differentiated by considering the carbonyl absorption peak as the carbonyl absorption peak of amide will be present at a lower wavenumber than the other.

b. Both the compounds are cyclic esters.

The CO absorption peak of smaller rings is present at a higher wavenumber.

Thus, the five-membered ester will show CO absorption at a higher wavenumber compared to the six-membered ester.

c. The secondary amide(-CONHR: one N-H ) shows one absorption peak, while the primary amide shows two absorption peaks(-CONH₂: two N-H bands)

d. The anhydride consists of two carbonyl groups and hence will show two CO absorption peaks while the acid chloride shows only one CO absorption peak.