Question

Question: How do the mechanisms of the following reactions differ?

Short answer

• This reaction follows two step nucleophilic aromatic substitution.

• This reaction follows S_N2 one step reaction mechanism.

Step-by-step solution

Nucleophilic Aromatic Substitution reaction (SNAr)

In nucleophilic aromatic substitution reactions, the ring has a leaving group that is replaced by a nucleophile.Nucleophilic aromatic substitution of pyridine takes place at C-2 or C-4 because addition to these positions leads to the most stable intermediate. Only when addition occurs to these positions, a resonance contributor obtained that has the greatest electron density on nitrogen, the most electronegative elementof the ring atoms.

It involves two steps:

1. The nucleophile added to the ring carbon that is attached to the leaving group.
2. The leaving group is eliminated in the last step of the reaction.

Nucleophilic aromatic substitution SN2

TheS_N2 reaction is a nucleophilic substitution reaction where bond is broken and other is form simultaneously. Two reacting species involved in the rate determining step of the reaction. The termS_N2 stands for substitution nucleophilic bimolecular.

Difference in mechanism of both the reactions

This reaction follows two step nucleophilic aromatic substitution (S_NAr).

This reaction follows one step nucleophilic substitution reaction S_N2 reaction mechanism.

Mechanism of reaction (2)