Two kinds of reaction are possible when a nucleophilic reagent attacks a substituted alkane. In nucleophilic substitutions the nucleophile displaces a weaker nucleophile from its bonded site. In elimination reactions, the nucleophile removes a Hydrogen from a neighbouring C-atom and causes elimination of the leaving group leading to the formation of an alkene. The reagents and conditions determine which reaction predominates. In this module, we will also present the key features of addition reactions, where electrophilic reagents interact with electron rich multiple bonds.