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Why is SN2 stereospecific?

Answer 1

Because the mechanism of the reaction determines the stereochemical outcome of the reaction.

A chiral centre of a given handedness will have an inverted handedeness upon #S_N2# reaction. I have always likened the mechanism to an umbrella blowing itself inside out on a windy day. Likewise its optical antipode will have the opposite handedness when it undergoes that same reaction

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Answer 2

Addison Armstrong

SN2 (Substitution Nucleophilic Bimolecular) reactions are stereospecific because the incoming nucleophile replaces the leaving group in a single concerted step, resulting in inversion of stereochemistry at the reaction center. This occurs due to the backside attack of the nucleophile on the electrophilic carbon, leading to the expulsion of the leaving group and the formation of a new bond. As a result, the configuration of the stereocenter is inverted, leading to retention of stereochemistry in the product.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.