Substituent Effect in Photochemistry of Carbonyl Compounds: α-Halovalerophenones

Valerophenones containing a substituent at alpha position to the carbonyl group show the remarkable substituent effects on their photochemical reactions. α-Bromovalerophenone gives only the C-Br bond cleavage products, but the α-chlorovalerophenone follows the classical Norrish/Yang reaction pathway predominantly