A biomolecular nucleophilic substitution reaction is a type of nucleophilic substitution whereby a lone pair of electrons on a nucleophile attacks an electron deficient electrophilic center and bonds ...A biomolecular nucleophilic substitution reaction is a type of nucleophilic substitution whereby a lone pair of electrons on a nucleophile attacks an electron deficient electrophilic center and bonds to it, resulting in the expulsion of a leaving group. It is possible for the nucleophile to attack the electrophilic center in two ways: Frontside vs. Backside Attacks
Instead, the formation of the σ_{C-Nuc} bond and the breaking of the σ_{C-LG} bond occur at the same time in what is known as a concerted mechanism. The reaction is 2 nd order because the rate...Instead, the formation of the σ_{C-Nuc} bond and the breaking of the σ_{C-LG} bond occur at the same time in what is known as a concerted mechanism. The reaction is 2 nd order because the rate of the reaction is dependent on the concentration of both the nucleophile AND the structure of the starting material. This means that the nucleophile must approach exactly 180° opposite of the direction of the leaving group, which is where the larger lobe of the σ^{*}_{C-X} lies.
