Walden inversion

Walden inversion is the inversion of a stereogenic center in a chiral molecule in a chemical reaction. Since a molecule can form two enantiomers around a stereogenic center, the Walden inversion converts the configuration of the molecule from one enantiomeric form to the other. For example, in an S_N2 reaction, Walden inversion occurs at a tetrahedral carbon atom. It can be visualized by imagining an umbrella turned inside-out in a gale. In the Walden inversion, the backside attack by the nucleophile in an S_N2 reaction gives rise to a product whose configuration is opposite to the reactant. Therefore, during S_N2 reaction, 100% inversion of product takes place. This is known as Walden inversion.

It was first observed by chemist

In this reaction, the silver oxide in the first step acts as a hydroxide donor while the silver ion plays no role in the reaction. The intermediates are the carboxyl dianion A which gives an intramolecular nucleophilic substitution by the β-carboxylate anion to produce a four-membered β-lactone ring B. The α-carboxyl group is also reactive but in silico data suggests that the transition state for the formation of the three-membered α-lactone is very high. A hydroxyde ion ring-opens the lactone to form the alcohol C and the net effect of two counts of inversion is retention of configuration.^[2]

See also

• Another demonstration of the Walden cycle in the Brook rearrangement.

References