Illustrated Glossary of Organic Chemistry

SN1 mechanism (SN1 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. SN1 is an abbreviation for 'substitution nucleophilic unimolecular' or 'substitution nucleophilic 1st order'.

Mixture of enantiomers
An intermolecular SN1 reaction.

An intramolecular SN1 reaction.