The bromide shown (two stereocentres, single stereoisomer) is treated with $NaI$ in acetone for a short time. Substitution occurs only at the carbon bearing Br, by $S X_{N} 2$ . Which structure is the product?

AStructure A
BStructure B
CStructure C
DStructure D

Answer: C

The compound is (2S,3S)-2-bromo-3-methylpentane.

S X_{N} 2

inverts only C2; C3 is not involved. Replacing Br by I in the same SMILES position and flipping the C2 tag gives C[C@@H](I)[C@@H](C)CC, in which C2 is inverted and C3 retained. The other structures invert both centres, retain both, or invert C3 only.

Practice Organic Reaction Mechanisms III: Nucleophilic Substitution More on Stereochemical outcome of substitution on drawn chiral substrates

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The bromide shown (two stereocentres, single stereoisomer) is treated with NaI in acetone for a short time. Substitution occurs only at the carbon bearing Br, by SXN​2. Which structure is the product?

Answer: C

More questions on Stereochemical outcome of substitution on drawn chiral substrates

The bromide shown (two stereocentres, single stereoisomer) is treated with $NaI$ in acetone for a short time. Substitution occurs only at the carbon bearing Br, by $S X_{N} 2$ . Which structure is the product?