Product studies and laser flash photolysis on alkyl radicals containing two different beta-leaving groups are consonant with the formation of an olefin cation radical

1-Bromo-2-methoxy-1-phenylpropan-2-yl (3) and 2-methoxy-1-phenyl-1-diphenyl phosphatopropan2-yl (4) were generated under continual photolysis from the respective PTOC precursors in a mixture of acetonitrile and methanol. The r adicals undergo heterolytic fragmentation of the substituent in the P-posit ion to generate the olefin cation radical (5). Z-2-Methoxy-1-phenylpropene (15) is the major product formed in the presence of 1,4-cyclohexadiene, and is believed to result from hydrogen atom transfer to the oxygen of the ole fin cation radical, followed by deprotonation. Laser flash photolysis exper iments indicate that reaction between 5 and 1,4-cyclohexadiene occurs with a rate constant of similar to6 x 10(5) M-1 s(-1). 2,2-Dimethoxy-1-phenylpro pane (18) is observed as a minor product. Laser flash photolysis experiment s place an upper limit on methanol trapping of 5 at k < 1 x 10(3) M-1 s(-1) and do not provide any evidence for the formation of reactive intermediate s other than 5. The use of two PTOC precursors containing different leaving groups to generate a common olefin cation radical enables one to utilize p roduct analysis to probe for the intermediacy of other reactive intermediat es. The ratio of 15:18 is dependent upon hydrogen atom donor concentration, but is independent of the PTOC precursor. These observations are consisten t with the proposal that both products result from trapping of 5 that is fo rmed via heterolysis of 3 and 4.