Photochemistry of valerophenone in solid solutions

Photoreactivity of valerophenone was investigated in frozen solid solvents: benzene, cyclohexane, t-butanol, hexadecane, and water. Different product and mass distributions were followed during the course of the photoreaction . It was evidenced that a portion of ketone molecules is almost unreactive in the solid state due to physical restraints of the solid solvent cavity. Free rotation along the C-C bonds becomes difficult inside the cavity and i t is probable that larger conformational changes are totally restricted. It was shown that a fraction of molecules having the favorable conformation f or hydrogen abstraction reacts with the same photochemical efficiency no ma tter what solvent was used. The elimination/cyclization ratio of the Norris h Type II reaction was studied as a function of temperature. Variation of t he ratios, characteristic for each solvent, diminished with decreasing temp erature what has been rationalized in terms of the effective reaction cavit y. The semi-empirical PM3 method and molecular mechanics MM3 force field ca lculations were performed to evaluate stabilities of the ground state valer ophenone conformations. (C) 2000 Elsevier Science S.A. All rights reserved.