The secondary allylic chloride shown (double bond geometry and configuration not specified) is hydrolysed in water by a pure $S X_{N} 1$ pathway. Assume the allyl cation is attacked by water at either terminus. Count every configurational stereoisomer (geometrical and optical, counted separately) of the constitution of the alcohol(s) that can form. Give your answer as an integer.

Numerical answer type, tolerance 0.5.

Answer: 4

The compound is 4-chloropent-2-ene. The allyl cation

CH X_{3} - CH = CH - CH X^{+} - CH X_{3} \leftrightarrow CH X_{3} - CH X^{+} - CH = CH - CH X_{3}

is symmetrical, so both termini give the same constitution, pent-3-en-2-ol. This has one stereocentre (C2) and one stereogenic double bond (E/Z), giving

2 \times 2 = 4

stereoisomers (checked with RDKit: 4). Answer: 4.

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Answer: 4

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