Front side
attack: In an ionic
substitution
reaction, approach of the nucleophile
to the same face of the molecule
as the existing (in SN2)
or former (in SN1)
carbon-leaving
group bond.
Causes retention
of
configuration at the carbon suffering substitution.
Front side attack on a tetrahedral carbon atom in the SN2 reaction mechanism.
Front side attack on a carbocation in the SN1 reaction mechanism.