Engineering reactions in crystalline solids: Predicting photochemical decarbonylation from calculated thermochemical parameters

A detailed thermochemical analysis of the a-cleavage and decarbonylation reactions of acetone and several ketodiesters was carried out with the B3LY-P/6-31G* density functional method. The heats of formation of several ground-state ketones and radicals were calculated at 298 K to determine bond dissociation energies (BDE) and radical stabilization energies (RSE) as a function of substituents. Results show that the radical-stabilizing abilities of the ketone substituents play a very important role on the thermodynamics of the a-cleavage and decarbonylation steps. An excellent correlation between calculated values and previous experimental observations suggests that photochemical a-cleavage and decarbonylation in crystals should be predictable from knowledge of excitation energies and the RSE of the substituent.