Answer:
Explanation:
In the attached file , the resonance structure of amide and ester has been given . One can find that due to oxygen being more electronegative than nitrogen , the contribution of second resonance structure is more . Hence the double bond character of carbonyl bond ( =C=O ) as double bond is less . It is more in the form of single bond . ( see the resonance structure )
On the other hand it is not so in ester because of absence of nitrogen atom. Here carbonyl group is more in the form of double bond . The stretching wave number for double bond is more because it has greater energy .
