Some considerations about the substituent effect on the infrared absorption intensities of symmetric stretching and bending vibrations of methyl group

Abstract

Infrared absorption intensities of symmetric stretching and bending modes of methyl group have been measured for 13 compounds. Quite different dependences of intensities on the substituents attached to methyl group have been observed for each of the two modes. The similarity of the intensity behaviours between the substituent and solvent effects has been referred to. The factors determining the intensity changes have been discussed in terms of the electric effects of substituents. Finally, it is demonstrated that the qualitative understanding of the different intensity behaviours observed for each of the modes is possible with the approximate application of the Valence—Optical theory.