X-ray structural studies on a series of oxygenated anthracene cycloadducts. Evidence for π-σ* negative homohyperconjugation in the ground state

Abstract

Application of the variable oxygen probe to low-temperature crystal data from the series of oxygenated anthracene cycloadducts 10-16, revealed a strong response of the C-OR bond distance in these structures to the electron demand of the OR group. It is believed that this represents the manifestation of π-σ* negative homohyperconjugation in the ground state. Ab initio molecular orbital calculations on the model system 18 provided further support for this.