Knowledge Bank

One important characteristic of the overtone absorption frequencies is its sensitivity not only to the C-II bond type but also to the conformational state of the C-H bonds. Different environments are seen to influence otherwise equivalent C-H bonds in such a way that their vibrational overtone resonances become $resolved.1$ We report here the overtone studies of a number of alkenes, ketones, others and amines measured by the intracavity photoacustic technique in the gas phase and supplemented by thermal lensing spectroscopy in the liquid phase. Two peaks are observed for the overtones of a methyl group in a strongly anisotropic electronic environment such as -C=C-, -C=C, $-O=CH3$ or $-N-CH3$. The overtone results are similar to the $""transeffect""2$ observed cloud is responsible for weakening the trans C-H bond in as adjacent methyl group. Such a study allows us to establish possible correlations of the overtone spectra with chemical bond strengths.