Illustrated Glossary of Organic Chemistry

SN2 mechanism (SN2 reaction): A substitution reaction mechanism featuring nucleophilic substitution at an sp3 carbon, with simultaneous carbon-nucleophile bond formation and carbon-leaving group bond scission. SN2 is an abbreviation for 'substitution nucleophilic bimolecular' or 'substitution nucleophilic 2nd order'.

A concerted SN2 reaction.

A nonconcerted (stepwise) SN2 reaction.

An intramolecular, concerted SN2 reaction.