Why do stronger nucleophiles favor SN2 reaction mechanism?

A stronger nucleophile is a highly electron rich or fully negative charge species. It has been experimentally found that the stronger nucleophile favor SN2 reaction mechanism.

They have a tendency to react with carbocation more quickly, before a leaving group would have a chance to dissociate and proceed through an SN1 reactionmechanism.

This is because of a stronger nucleophile is closer in energy to the transition state, which lower the activation energy giving a faster SN2 reaction.

Read more: What is ethylene oxide or oxiran?

But a weaker nucleophile is farther in energy to the transition state, which raises the activation energy giving a slower SN2 reaction.

In other words, the bimolecular transition state is of lower energy than the unimolecular transition state. For the above said reason, stronger nucleophiles favor SN2 reaction mechanism.

For example, OHㄧ is a strong nucleophile. When it participates in nucleophilic substitution reaction with methyl bromide, OH ̄prefers SN2 reaction mechanism.

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