In electrophilic addition to carbon-carbon double bonds, a positive species approaches in the first step converting the pair of π-electrons into an s-pair. As in electrophilic substitution, the approaching species need not actually be a positive ion but may be the positive end of a dipole or induced dipole.
Bromohydrin formation is an example of electrophilic addition to an alkene initiated by attack of a proton and subsequent reaction with bromide ion. This reaction is stereospecific and is an example of anti-addition. Thus, reaction of a C=C bond in the intermediate (I) with HBr results in the stereospecific formation of the bromohydrin (II). This compound may subsequently be converted to the antimitotic drug Podofilox (III).