Question

Distinguish between – S_N1 and S_N2 mechanism of substitution reaction ?

Answer 1

Factor	SN1	SN2
(1) Number of steps	Two steps	One step
(2) Molecularity/Order	Unimolecular/1st order	Bimolecular/2nd order
(3) Reaction rate	Depends upon concentration of one reacting species	Depends upon concentration of two reacting species
(4) Attack of a nucleophile	Back side attack and front side attack on a substrate with equal probability	Only back side attack on a substrate
(5) Transition state	Two steps, two transition states	One step, one transition state
(6) Type of substrate	Mainly tertiary (3°) substrate	Mainly primary (1°) substrate
(7) Stereochemistry	50% inversion and 50% retention of configuration	100% inversion of configuration
(8) Enantiomer	Forms racemic mixture	Forms opposite enantiomer
(9) Solvent	Polar solvent favourable	Nonpolar solvent favourable
(10) Energy of activation	Two values of energies of activation	One value of energy activation
(11) Intermediate	Carbocation intermediates	No intermediate
(12) Nucleophile	Weak nucleophile favourable	Strong nucleophile favourable
(13) Order of reactivity in alkyl halides	Tertiary > Secondary > Primary	Primary > Secondry > Tertiary