Summary of Benzene Ring Group Frequencies

The group frequencies of aromatic compounds near 1600 cm are excellent for recognizing the presence of aromatic rings in the spectrum of an unknown compound, although some olefinic nitro, amino, and carbonyl compounds can also have bands there. 

A compound such as H3N —SOJ can have a strong band near 1600 cm that is representative of the NHJ group. This band could thus be easily misidentified as a ring vibration. 

In a biphenyl derivative where each ring is substituted in a different manner, characteristic group frequencies for each ring should be present in the spectrum. 

A conjugated aromatic ring normally has a band near 1585 cm , while an unconjugated ring has one near 1600 cm However, many aromatic compounds can have bands which appear between these two frequencies. For example. 

Some nonaromatic structures which have absorption bands in the 1600-1450 cm region include the NH2 group, which has a band near 1600 cm the NH and NH groups, which have bands 

---