SPATIAL AND ELECTRONIC-STRUCTURE OF VINYL -CHALCOGENIDES AND ALLENYL-CHALCOGENIDES

Alkyl vinyl chalcogenides are characterised by a complex pattern of ro tational isomerism and have several types of stable conformers. The pe culiarities of conformational structure of these compounds can be uder stood only by consideration of the whole set of steady states. Conform ational analysis of divinyl chalcogenides gives evidence that the surf ace of potential energy of internal rotation is not to be regarded as simply a source of information on rotational isomerism, but rather as a tool of search for steady states corresponding to certain ranges of changing the inner molecular co ordinates. Main patterns of the orbita l structure of allenyl ethers and vinyl chalcogenides have been discus sed, icluding the poor dependence of both the structure and relative a rray of upper occupied pi-MO of alkyl vinyl chalcogenides on the natur e of heteroatom and the structure of alkyl substituent. The low energy excited state of sigma-symmetry presents a common feature of vinyl ch alcogenides. The pi-symmetry excited states of these compounds are loc ated on the energy scale invariably above than the sigma-symmetry stat es.