Question

For each of the major absorption peaks that you have identified in the IR spectra of methyl benzoate and your triphenylmethanol derivative, list the frequencies and functional group to which it corresponds to.

Answer 1

  

IR frequences and corresponding functional groups

3100-3000 cm−1(w)	Aromatic C-H stretch
2960 and 2870 cm−1(m)	Methyl C-H stretch
1730-1715 cm−1(s)	Conjugated ester C=O stretch
1600-1585 cm−1(m) and 1500-1400 cm−1(m)	Aromatic C-C stretch
1380 cm−1(w) and 1260 cm−1(m)	C-O stretch
750-700 cm−1(s) and 710-690 cm−1(m)	Aromatic C-H 'out-of-plane' bend

The structure of methyl benzoate is

OCH3

It has a monosubstituted benzene ring, an ester group, and a methyl group.

1. C-O stretching

The strongest peak should be the ester C=O stretch.

This normally appears at 1750-1735 cm−1, but conjugation with the ring shifts the peak to 1730-1715 cm−1.

There should also be one medium and two strong bands in the region from 1300-1000 cm−1.

The two strong bands arise from the symmetric and antisymmetric C-O stretches of the ester COO group, and the weaker band is the ether CO stretch of the OCH3 group.

Triphenylmethanol IR major peaks:
An alcohol (-OH) peak should be around 3550-3200 cm-1. It must be a broad. Its a major peak
  also you can see C-O peak around 1300-1000 cm-1