( 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