Question

briefly explain why Sn2 reactions are favored using strong nucleophiles while Sn1 reactions are not necessarily dependent on nucleophilic strength

Answer 1

Sn2 reactions are concerted reaction. rate equation is given by

Rate = k [electrophile] [Nucleophile]

Sn1 reactions are stepwise mechanism. rate equation is given by

Rate = k [electrophile]

Here Nucleophile is base. In the rate determing step, nucleophile will participate. Hence strength of nucleophile (Base) is necessary to proceed the reaction faster. But in SN1 reaction, nucleophile will not be participating in the rate. Hence rate of the reaction purely depends on electrophile. Hence nucleophilic strength is not necessary.