On the possibilities of π-ylides

A systematic survey of substituted annulenes, using zeroth order Hückel theory, has uncovered a subclass of such structures which are predicted to have very substantial charge separation. An examination of selected structures by MNDO semi-empirical molecular orbital computations provided support for the Hückel descriptions. Such compounds may be of immediate interest to those pursuing synthetic or mechanistic problems which involve cycloaddition reactions. Keywords: π-ylides.