Theoretical studies on the ultraviolet spectra of five-membered heterocycles. π-Systems isoelectronic with condensed aromatic hydrocarbons

Abstract

A single theoretical scheme has been suggested for the interpretation of the u.v. spectra of five-membered heterocycles condensed with aromatic rings: this scheme consists in considering each group of π-isoelectronic heterocompounds as a series in which the spectral features vary between those of two extreme reference hydrocarbons, the former containing the cyclopentadiene-type ring, the latter the CHCH group in place of the heteroatom. The assumptions have been confirmed by a semiempirical SCF–Cl calculation procedure and the sequence O, S, and HN has been found for the hetero-derivatives in all the series.