Intro to addition reactions

when an alkene is reacted with reagent X-Y, the reverse reaction of an elimination takes place and you get a disubstituted alkane (monusubstituted in the case where X or Y is a hydrogen, or just an alkane if X-Y is H-H). Regiochemically, if the reagent is an acid, H-X, then the markovnikov alkyl halide is preferentially formed (with the halogen binding to the more substituted of the sp2 carbons). Stereochemically, X and Y can add in the same plane (Syn) or one from above and one from below (anti).