#cehmistry

In the SN2 reaction, the nucleophile performs a backside attack —that is, while the halide is still bonded to the alkyl chain, the nucleophile attacks the alkyl chain from behind, causing it to eject the original halide to which it was bonded. This works best when the alkyl chain is too unstable to form a carbocation and thus must always have a nucleophile attached to it. The nucleophile that does the backside attack should be more attractive to the alkyl chain involved. The solvent in which the reaction takes place should be aprotic, meaning the original halide is left alone and unpaired after the reaction.