Circular Dichroism. LXXIV.CD of Benzene Derivatives with Several Identical Chiral Substituents

Abstract

Abstract A comparison of the CD‐ and UV‐spectra of benzene derivatives, which are mono‐, 1,4‐di‐ or 1,3,5‐trisubstituted by (identical) chiral ligands, revealed that the rotational strength within the α‐band of mono‐ and 1,3,5‐trisubstituted benzenes is mainly derived from the magnetic transition moment of the benzene chromophore perpendicular to the ring, and from a corresponding electric transition moment stolen from a ligand transition. For the 1,4‐disubstituted homologues, the main contribution to the rotational strength is associated with the electric transition moment in the plane of the benzene chromophore and with a corresponding magnetic transition moment, stolen from the A 1g → E 1g (D 6b ‐notation) transition within the same ring. For the 1,3,5‐trisubstituted compounds, the 0–0‐band is scarcely, or not at all, detectable in the UV‐spectra, but distinctly recognizable in the CD‐spectra. In a few cases Cotton‐effects between the positions of the α‐ and the p‐bands could be detected, which are ascribed to the magnetically allowed A 1g → E 1g (D 6b ‐notation) transition.