Differing substituent effects on rates and regioselectivities in the di-π-methane rearrangement. New photochemical theory: excitation distribution (the ΔP matrix), reaction inhibition by vertical excited state stabilisation, ground Vs. excited state control

Abstract

A consistent pattern of control of regioselectivity by substituents was observed in three di-π-methane systems while the effect on rates varied with the system; from this three new concepts were derived: (i) a method allowing one to discern how excitation energy is partitioned throughout a molecule initially and during transformation to product, (ii) evidence that excessive vertical excited state stablization can inhibit reactions, (iii) exercise of excited or ground state substituent effects on a reaction depending on whether the unit bearing the substituent is appreciably excited at the critical point on the reaction hypersurface.