Photolysis of acetophenone derivatives with α‐cyclopropyl substituents

Laser flash photolysis of cyclopropyl(phenyl)methanone 6 in argon‐saturated methanol yields the triplet ketone (T 1K ) of 6 that is formed with a rate constant of ~1.7 × 10 7  s −1 ( λ max  = 360 nm) and has a lifetime of ~1.4 µs. T 1K of 6 decays to form ketyl radical 7 ( λ max ~300 nm), which dimerizes to form photoproducts, pinacol derivatives 8 and 9. In comparison, photolysis of trans ‐phenyl(2‐phenylcyclopropyl)methanone 1 in argon‐saturated chloroform‐d results in cis ‐phenyl(2‐phenylcyclopropyl)methanone 2 and a smaller amount of 3, presumably through 1,3‐biradical 11. Nanosecond laser flash photolysis of 1 does not reveal significant transient absorption, although the T 1K of 1 is detected with phosphorescence at 77 K. Density functional theory calculations were used to elucidate the triplet reactivity of 1, 2 and 6 by comparing the feasibility of H atom abstraction, cyclopropyl cleavage and β‐quenching of their triplet ketones. Copyright © 2014 John Wiley & Sons, Ltd.