Vibronic fine structure of formally forbidden transitions in circular dichroism

Abstract

The circular dichroism spectra of a number of aromatic compounds, in which the electronic transition at ca. 260 nm shows vibronic fine structure, are presented. A shift between the predominant maxima of the ultra-violet absorption band and the maxima of the circular dichroism band of compounds of the type C₆H₅CR₁R₂R₃ is observed, and the different vibrations involved in the ultra-violet and circular dichroism spectra are assigned. Comparison of the vibronic fine structure of the ultra-violet and circular dichroism spectra of the n→π^* CO transition of camphor and of isoandrosterone shows that the ultra-violet and circular dichroism maxima occur at the same frequencies.