In an SN2 reaction the configuration at the reacting carbon atom is
- A. inverted, because the nucleophile attacks from the side opposite the leaving group
- B. retained completely
- C. randomised, giving a racemic mixture
- D. unchanged because no bond is broken
Explanation
Back side attack turns the three remaining groups inside out like an umbrella in the wind, so an optically active substrate gives a product of opposite configuration, an effect called Walden inversion. An SN1 reaction gives a racemic mixture instead, because the planar carbocation can be attacked equally from either face. Stereochemistry is therefore the clearest experimental way to distinguish the two mechanisms.
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