Chapter 6 - IR and Raman Spectra–Structure Correlations: Characteristic Group Frequencies

Abstract

A general survey of important spectra–structure correlations for the IR and Raman spectra of organic molecules are discussed in detail. The characteristic group frequencies of both IR and Raman spectroscopy are complementary and their respective strengths and weaknesses are discussed for various functional groups. Using both techniques may provide confirmation of the presence of particular functional groups or provide additional information. Often bands for functional groups that are weak or inactive in the IR may exhibit strong bands in the Raman spectra. Skeletal vibrations typically provide more intense Raman bands than are encountered in the IR spectra. The functional groups discussed include X–H type stretches, aliphatics, conjugated aliphatics and aromatics, heterocyclic aromatics, five-membered ring heterocyclic aromatics, carbonyl compounds, alcohols, ethers and amines, NO, azo and CN type species, halogen compounds, sulfur containing compounds, and organic phosphorus compounds. Lastly a brief overview of the vibrational spectroscopy of inorganic compounds is presented. Idealized IR and Raman spectra as well as tables of characteristic group frequencies are provided. Each section is bookmarked to selected reference IR and Raman spectra that have been fully interpreted.