Illustrated Glossary of Organic Chemistry

S_N1 mechanism (S_N1 reaction): A substitution reaction mechanism featuring nucleophilic substitution at an sp³ carbon, in which carbon-nucleophile bond formation and carbon-leaving group bond scission are not simultaneous (i.e., the reaction is never concerted). The mechanism always includes a carbocation intermediate. S_N1 is an abbreviation for 'substitution nucleophilic unimolecular' or 'substitution nucleophilic 1^st order'.

Mixture of enantiomers

An intermolecular S_N1 reaction.


An intramolecular S_N1 reaction.