( b) SN2 type( Bimolecular nucleophilic substitution) These reactions proceed in one step and is a second order reaction with r = k [ RX ] [ Nu ].
During SN2 reaction, inversion of configuration occurs( Walden inversion) i. e., starting with dextrorotatory halide a laevo product is obtained and vice-versa, e. g.,
Reactivity of halides towards SN2 mechanism is 1 ° > 2 ° > 3 °
Rate of reaction in SN2 mechanism depends on the strength of the attacking nucleophile. Strength of some common nucleophiles is
: CN- >: I- >: OR- >: OH- > CH 3 COO: > H2O > F-
Non-polar solvents, strong nucleophiles and high concentration of nucleophiles favour SN2 mechanism.
Relative rates of some alkyl halides in SN1 and SN2 reactions are in the order