Amides & Lactams (RCONR₂)
1° & 2°-amides
3°-amides
6-membered lactams
5-membered lactams
4-membered lactams

C=O bands
1510 to 1700 cm^-1 (2 bands)
1650± 15 (one band)
1670 ± 10 (one band)
1700 ± 15
1745 ± 15

The effect of conjugation is much less than for aldehydes & ketones.  The higher frequency absorption (1665± 30) is called the Amide I band. The lower frequency Amide II band (1620± 30 in 1° amides & 1530± 30 in 2° amides) is largely due to N-H bending trans to the carbonyl oxygen. In concentrated samples this absorption is often obscured by the stronger amide I absorption. Hydrogen bonded association shifts some of these absorptions, as well as the prominent N-H stretching absorptions.  N-H stretch: 3170 to 3500 cm^-1. Two bands for 1°-amides, one for 2°-amides.