Recent studies by ingly demonstrated that the benzylic cations (1) rather Fahey and Schneider' and by Yates and Rolston 3y4 have convincpolar bromination of styrene derivatives proceeds through open than cyclic bromonium ions (2). These findings are further supported by the more recent work of Wilkins and Regulski5 and Yates and McDonald.6 Thus bromination of simple styrene derivatives proceeds nonstereoselectively2'3, although the trnns adduct is favored. In acetic acid, solvent attack occurs exclusively at the benzylic position3, and kinetic evidence of m-and e-substituted styrene derivatives yields P values characteristic of benzyl cation formation. 4 Although modest, an a-secondary isotope effect is found for these reactions.5 Despite the compelling evidence against bridging from studies of electronic factors, stereochemical evidence has led most researchers to favor a partially bridged species such as (3). Dubois et al 7 --* 3 however, contend that their kinetic results on the Br I A&l--&-R