The photochemical a cleavage and reduction reactions of several aryl alkyl ketones have been investigated. Electron-releasing aromatic substituents decrease the excited state reactivity of ieri-alkyl aryl ketones toward both primary photoprocesses to a similar extent. The aromatic carbonyl 3(n, π∗) state is concluded to be responsible for a cleavage as well as hydrogen abstraction reactions. The rate constant for intermolecular hydrogen abstraction by the carbonyl triplet state decreases with α-methyl substitution. Pinacol and carbinol products are formed via the combination and disproportionation of ketyl radicals. A primary deuterium isotope effect on isobutyrophenone ketyl radical disproportionation of 2.7 is observed. α-Methyl substituents increase the percentage of carbinol products due to steric hindrance of free-radical combination.
ASJC Scopus subject areas
- Organic Chemistry