Some aspects of Di-pi-methane rearrangement

Ferreira, Aurelio Baird Buarque (1976) Some aspects of Di-pi-methane rearrangement. University of Southampton, Doctoral Thesis.

Abstract

Two compounds were chosen for studies of substituent effects on the di-a-methane photochemical rearrangement: 1,l-dicyano-2-methyl-3-phenylprop-l-ene and trans-l-cyano-2-methyl-3-phenylprop-l-ene. Methylation and a dimethylation at the benzylic position, and ring-substitution with a range of electron-donating and withdrawing groups, provided the requiredseries of related compounds for study.The following information was then obtained for those compounds:a) the nature of the products of irradiation; b) the quantum yields of product formation in different solvents; c) fluorescence spectra, quantum yields and lifetimes - for the fluorescing compounds.Some ideas were provided for nterpreting the results obtained, with the use of postulated intermediates. Attempts were made to describe the interplay of the different mechanistic factors at the level of the potential energy surfaces of the reacting molecules.The most important result in the photochemistry of the compounds derived from 1,1-dicyano-2-methyl-3-phenylprop-l-one by rind!-substitution, is a decrease in the reaction quantum yields with the increase of electron donating character of the substituent. This we ascribe to a competition process of charge-transfer, leading to deactivation of the excited molecule. The compounds derived from trans- l-cyan o-2-methyl-3-phenyl prop-l-ene by ring-substitution did not show this regularity in their behaviour. The effect of methylation and dimethylation in both cases was an enhancement of the di-n-methane reactivity, but the finer details of this effect did not follow precisely the current views on the subject.

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