ENANTIOMER AND DIASTEREOISOMER RESOLUTION, ROTATIONAL BARRIERS, AND CD AND UV SPECTRA OF SOME TWISTED PUSH-PULL ETHYLENES

Suitably substituted twisted push-pull ethylenes capable of existing e ither as mixtures of achiral diastereoisomers or as pairs of enantiome rs have been resolved, in the first case into diastereoisomers by HPLC on silica, in the second case into enantiomers by chiral chromatograp hy on tris(phenylcarbamoyl)cellulose. Free energy barriers to rotation through the planar state have been determined by monitoring respectiv ely the rate of diastereoisomer interconversion and the rate of racemi zation at elevated temperatures. UV and CD spectra have been analysed with the aid of CNDO/S calculations for simplified models.