Illustrated Glossary of Organic Chemistry

Retention of configuration: A process in which the relative configuration or absolute configuration of an atom is retained. If the atom in question is a stereocenter, retention of configuration usually (but not always) changes an R absolute configuration into R, and S into S.

Hydrolysis of (S)-2-iodo-2-phenylbutane via the SN1 mechanism gives two products: (S)-2-phenyl-2-butanol (from retention of configuration) and (R)-2-phenyl-2-butanol (from inversion of configuration):

H2O
+
(S)-2-iodo-2-phenylbutane
(S)-2-phenyl-2-butanol
From retention of configuration
(R)-2-phenyl-2-butanol
From inversion of configuration

Hydrolysis of cis-4-tert-butyl-1-iodo-1-methylcyclohexane via the SN1 mechanism demonstrates change in configuration when the leaving group is not bonded to a stereocenter. The products are cis-4-tert-butyl-1-methylcyclohexanol (from retention of configuration) and trans-4-tert-butyl-1-methylcyclohexanol (from inversion of configuration):

H2O
+
Cis-4-tert-butyl-1-iodo-1-methylcyclohexane
Cis-4-tert-butyl-1-methylcyclohexanol
From retention of configuration
Trans-4-tert-butyl-1-methylcyclohexanol
From inversion of configuration