SNi

A typical representative organic reaction displaying this mechanism is the chlorination of alcohols with thionyl chloride, or the decomposition of alkyl chloroformates, the main feature is retention of stereochemical configuration.

The second step is the loss of a sulfur dioxide molecule and its replacement by the chloride, which was attached to the sulphite group.

The difference between SN1 and SNi is actually that the ion pair is not completely dissociated, and therefore no real carbocation is formed, which else would lead to a racemisation.

[citation needed] This reaction type is linked to many forms of neighbouring group participation, for instance the reaction of the sulfur or nitrogen lone pair in sulfur mustard or nitrogen mustard to form the cationic intermediate.

When the solvent is also a nucleophile such as dioxane two successive SN2 reactions take place and the stereochemistry is again retention.

SNi reaction mechanism Sn1 occurs in tertiary carbon while Sn2 occurs in primary carbon
S N i reaction mechanism Sn1 occurs in tertiary carbon while Sn2 occurs in primary carbon