What stereochemical outcome characteristically results from an S_N2 nucleophilic substitution reaction at a chiral center?
Answer and explanation
Correct answer: B. Complete inversion of configuration (Walden inversion)
- Step 1: In an S_N2 reaction, the nucleophile attacks from the side directly opposite the departing leaving group (backside attack). Step 2. This umbrella-like flipping of bonds causes 100% inversion of stereochemical configuration (Walden inversion). Answer: Complete inversion of configuration (Walden inversion). Why not the others: Complete retention occurs in S_Ni; racemization occurs in S_N1 through planar carbocations; meso requires symmetric achiral molecules.
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