The compound shown (its configuration is not specified) undergoes SN2 with $NaCN$ only at the carbon-bromine bond; the C-Cl bond is untouched and elimination is ignored. Counting enantiomers as separate stereoisomers, how many stereoisomers does the constitution of the substitution product have? Answer as an integer.

Numerical answer type, tolerance 0.5.

Answer: 4

Only Br is replaced by CN, giving 3-chloro-2-methylpentanenitrile, CH3CH2CHCl-CH(CH3)-CN. It has two stereocentres (C-2 and C-3) and no symmetry, so the stereoisomers are

2^{2} = 4

(two enantiomeric pairs); RDKit enumeration gives 4.

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