POLAR ADDITIONS TO STYRENE AND 2-BUTENE SYSTEMS .I. DISTRIBUTION AND STEROCHEMISTRY OF BROMINATION PRODUCTS IN ACETIC ACID

The products of bromine addition in acetic acid have been investigated for a series of ten ring- and side-chain-substituted styrenes and for cis- and trans-2-butenes. The styrenes generally give substantial amounts of acetoxy bromides as well as the expected 1,2-dibromides, but the butenes give almost exclusively dibromide under the same conditions. The acetoxy bromides isolated are shown to be the 1-acetoxy-2-bromo derivatives, with one exception. The additions to the styrenes are nonstereospecific, although trans addition is favored, whereas additions to cis- and trans-2-butenes are completely stereospecific and trans. Acetoxy bromide formation was found to be more stereoselective than dibromide formation. The results are taken as evidence that the intermediates formed in the styrene reactions resemble open α-phenylcarbonium ions more than bromonium ions. © 1969, American Chemical Society. All rights reserved.