i didn't understood the meaning of SN1 and SN2 rxn mechanisms

Dear Student

 

Nucleophilic substitution is the reaction of an electron pair donor (the nucleophile, Nu) with an electron pair acceptor (the electrophile). An sp³-hybridized electrophile must have a leaving group (X) in order for the reaction to take place.

 

The term S_N2 means that two molecules are involved in the actual transition state:

The departure of the leaving group occurs simultaneously with the backside attack by the nucleophile.

The S_N2 reaction thus leads to a predictable configuration of the stereocenter - it proceeds with inversion (reversal of the configuration).

In S_N1 reactions means nucleophilic substitution unimolecular. The reaction rate depends only on the concentration of the reactant and not on the nucleophile.

In the S_N1 reaction, a planar carbenium ion is formed first, which then reacts further with the nucleophile. Since the nucleophile is free to attack from either side, this reaction is associated with racemization.

We hope that clarifies your query.

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Team

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