Intensities of some group characteristic infra-red bands

Molar-intensity data have been obtained, both as peak extinction coefficients and as band areas, for several infra-red bands known to be characteristic of chemical groups. In view of the fact that many compounds are insoluble in spectroscopically suitable solvents, the substances were measured as solids in potassium bromide disks. The bands considered were CN stretching band in nitriles, the CO stretching band in esters, ketones, amides, acids and salts, the NO stretching bands in nitro compounds, and the SO stretching bands in sulphones, sulphonamides and sulphonic acids. About twenty compounds were examined in each case.The usefulness of such data in analysis and structural diagnosis has been considered. It was concluded that, provided the total area under the band, rather than the peak-extinction coefficient is used as the measure of intensity, reasonably constant intensity factors could be assigned to several of the above characteristic bands. The significance of this is that rough quantitative estimates of the concentrations of certain groups in material of unknown structure can be made, and that intensity measurements may be used to supplement structural diagnosis from band frequencies.