For SN1, what stereochemical outcome is observed when starting from a chiral substrate?

• A. Racemization due to planar carbocation
• B. Retention of configuration
• C. Inversion of configuration
• D. No reaction

Answer: (A)

The key idea is that SN1 reactions proceed by forming a carbocation. Once the leaving group departs, you get a planar, sp2-hybridized carbocation. A planar intermediate has no defined “top” or “bottom” face, so the nucleophile can attack from either side with equal likelihood. If the starting carbon was chiral, this loss of stereochemical information during carbocation formation means the product is produced as a 1:1 mix of enantiomers—racemic. So the stereochemical outcome is racemization due to the planar carbocation.

In contrast, SN2 involves backside attack that inverts configuration, and “no reaction” would only be correct if ionization never occurs under the given conditions. Retention would require unusual neighboring-group effects, which go beyond the standard SN1 picture, so they’re not the typical outcome here.