Question

The IR spectra shown next may include a carboxylic acid, an ester, an amide, a nitrile, an acid chloride, or an acid anhydride.

Determine the functional group suggested by each spectrum, and list the specific frequencies you used to make your decision.

Short answer

(a) Single C=O at of the acid chloride.

(b)There is one broad peak at which is of the C=O of the primary amide and two peaks between which is of the N-H bonds.

(c) Two absorption bands of C=O at and which is of the anhydride functional group.

Step-by-step solution

About IR spectrum

A spectroscopic technique that has a significant role in identifying the functional group present in organic compounds is IR spectroscopy.

The functional groups exhibit characteristic absorption bands at a certain wavelength. Depending on the wavelength, the functional groups can be identified.

About the IR spectrum (a)

The frequency present in the spectrum (a) is . There is a very sharp peak at this frequency. This frequency is of C=O of an acid chloride. There are no other carbonyl groups that show high frequency.

About the IR spectrum (b)

There is one broad peak at which is of the C=O of the primary amide. There are two peaks between which is of the N-H bonds.

About the IR spectrum (c)

There are two absorption bands of C=O that occur at and which is of the anhydride functional group.