Solvolyses of some 13C- or 14C labeled triarylvinyl bromides in aqueous acetic acid

Article abstract of DOI:10.1139/v86-205

The presence of different amounts of added LiClO4 in the solvolysis of triphenyl<2-14C>vinyl bromide (1-Br-2-14C) or trianisyl<2-14C>vinyl bromide (2-Br-2-14C) in 70percent HOAc did not materially affect the extent of scrambling of the label arising from 1,2-aryl shifts in the triarylvinyl cation or k_r, the rate constant for the 1,2-aryl shift.Solvolysis of a 2:3 mixture of (E)- and (Z)-1,2-diphenyl-2-tolylvinyl bromide ((E,Z)-3-Br) in 70percent HOAc gave an 81:15 mixture of 1,2-diphenyl-2-tolylethanone (5) and 2,2-diphenyl-1-tolylethanone (6), the latter product, 6, being derived from a 1,2-phenyl shift in the 1,2-diphenyl-2-tolylvinyl cation to the more stable 2,2-diphenyl-1-tolylvinyl cation.With (E,Z)-3-Br-2-13C as substrate and analysis by gc-ms, about 26-27percent scrambling of the 13C label was found in both products, 5-1,2-13C and 6-1,2-13C.Solvolyses of (E,Z)-3-Br-2-13C in 50percent and 70percent HOAc showed that the extent of scrambling in the major products, 5-1,2-13C, was lower in 50percent HOAc than in 70percent HOAc, similar to a trend previously observed for solvolyses of 1-Br-2-14C.In contrast, solvolyses of 2-Br-2-14C in 50, 70, or 90percent HOAc gave essentially the same extent of scrambling.Mechanistic implications of these results are discussed.