Steric effects on the ultraviolet spectra of monoarylphosphines

Abstract

The u.v. absorption spectra have been determined for a series of primary, secondary, and tertiary monoarylphosphines in which the aryl group varies through phenyl, o-tolyl, m-tolyl, p-tolyl, and mesityl, and the phosphorus substituents through H, Me, Et, Prⁱ, and Bu^t. The spectra contain a charge-transfer band which is sensitive to steric effects. The spectra show that the amount of conjugation of the phosphorus lone-pair of electrons with the aryl ring is small and is reduced still further by steric crowding. The possible conformational changes induced by the steric effects are discussed.