Photochemistry of valerophenone in solid solutions

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 2000-06, Vol.134 (1), p.37-44
• Main Authors: Klán, Petr, Janošek, Jaroslav, Křı́ž, Zdeněk
• Format: Article
• Language: English
• Subjects: Conformational search; Effective reaction cavity; Norrish Type II reaction; Organized media; Photochemistry; Solvent effects; Valerophenone
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/S1010-6030(00)00244-6

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 it is probable that larger conformational changes are totally restricted. It was shown that a fraction of molecules having the favorable conformation for hydrogen abstraction reacts with the same photochemical efficiency no matter what solvent was used. The elimination/cyclization ratio of the Norrish Type II reaction was studied as a function of temperature. Variation of the ratios, characteristic for each solvent, diminished with decreasing temperature what has been rationalized in terms of the effective reaction cavity. The semi-empirical PM3 method and molecular mechanics MM3 force field calculations were performed to evaluate stabilities of the ground state valerophenone conformations.