when an alkene is reacted with a haloacid, H-Cl, H-Br, or H-I, the pi-bond acts as a base and takes the proton from the acid, forming a halide ion and a carbocation on the more substituted position. If a more stable cation is possible through 1,2-hydride shift or 1,2-methide shift, then rearrangement takes place. The halide ion attacks the carbocation to form a racemic mixture of (R) and (S) alkyl halides, assuming a chirality center is formed.
