a) Briefly explain S_N^2 mechanism with an example. b) In dehydrohalogenation of 2-Bromopentane why Pent-2-ene is major product

Question

On kinetic consideration, nucleophilic substitution in aryl/alkyl halides may be S_N1 or S_N2 mechanisms.

a) Briefly explain S_N2 mechanism with an example.

b) In dehydrohalogenation of 2-Bromopentane why Pent-2-ene is major product and Pent-ene is minor product.

Answer 1

a) S_N2 mechanism (bimolecular nucleophilic substitution)

1. Takes place in a single step

2. Through the formation of the intermediate transition state

3. Inversion of configuration occurs

b) Saytzeff Rule: In dehydrohalogenation reaction, the more substituted alkene is the major product.