Bromohydrin formation in aqueous dimethyl sulphoxide; electronic and steric effects

Abstract

The role of electronic and steric effects in the stereospecific trans-addition of the elements of hypobromous acid (HOBr) to a selected group of olefins, with moist dimethyl sulphoxide as solvent-reactant and N-bromosuccinimide as the source of bromine, has been examined. In the absence of severe steric restrictions, the electronic effects have been observed to direct the addition in a Markownikoff sense. Highly hindered olefins and those wherein the electron density at the carbon–carbon double bond is severely depleted by electron-withdrawing substituents fail to react. Similar systems which have shown a susceptibility to carbonium ion rearrangements in analogous reactions fail to yield, for the most part, rearranged products. The intermediate is deemed best represented by a bromonium ion, symmetrical or non-symmetrical, depending upon the structure of the starting olefin. If the addition of the elements of HOBr is retarded owing to electronic or steric effects, considerable amounts of dibromide accompany bromohydrin.