In organic and inorganic chemistry, nucleophilic substitution is a fundamental class of substitution reaction in which an "electron rich" nucleophile selectively bonds with or attacks the positive or partially positive charge of an atom attached to a group or atom called the leaving group; the positive or partially positive atom is referred to as an electrophile. The most general form for the reaction may be given as Nuc: + R-LG → R-Nuc + LG:
The electron pair (:) from the nucleophile (Nuc) attacks the substrate (R-LG) forming a new bond, while the leaving group (LG) departs with an electron pair. The principal product in this case is R-Nuc. The nucleophile may be electrically neutral or negatively charged, whereas the substrate is typically neutral or positively charged. Nucleophilic substitution at saturated carbon centres
SN1 and SN2 reactions
In 1935, Edward D. Hughes and Sir Christopher Ingold studied nucleophilic substitution reactions of alkyl halides and related compounds. They proposed that there were two main mechanisms at work, both of them competing with each other. The two main mechanisms are the SN1 reaction and the SN2 reaction. S stands for chemical substitution, N stands for nucleophilic, and the number represents the kinetic order of the reaction. A graph showing the relative reactivities of the different alkyl halides towards SN1 and SN2 reactions
An example of nucleophilic substitution is the hydrolysis of an alkyl bromide, R-Br, under alkaline conditions, where the attacking nucleophile is the OH− and the leaving group is Br-. R-Br + OH− → R-OH + Br−
Nucleophilic substitution reactions are commonplace in organic chemistry, and they can be broadly categorised as taking place at a saturated aliphatic carbon or at (less often) a saturated aromatic or other unsaturated carbon centre.
Nucleophilic substitution is the reaction of an electron pair donor (the nucleophile, Nu) with an electron pair...