2.2 Group Regions

Though the vibrational structure of a molecule may be quite complex, some generalizations are possible. These are based on the notion of functional groups and similar structural features. The correlation of common structural units to their corresponding IR absorptions gives rise to group regions. A group correlation chart shows the more common regional assignments. Group correlation charts can be obtained from

IR Correlation Chart PDF file

IR Group Correlation Web Page

General IR Site including links to correlation charts

General IR Site including links to correlation charts

Some key points should be kept in mind about spectroscopic assignment based on group correlations:

• Some regions are more reliable than others.
• Many regions overlap
• An absorbance in a region does not conclusively indicate the presence of a particular structural feature.
• Detailed analysis and assignment is in fact possible, but usually requires extensive experimentation.