3-Chlorobut-1-ene, $CH X_{2} = CH - CH (Cl) - CH X_{3}$ , is heated in neutral water, where it ionises (SN1) to an allylic carbocation that is captured by water. Ignoring elimination and any further reaction, how many different alcohols can be formed if every structurally possible stereoisomer (each enantiomer of the chiral alcohol and each E/Z isomer) is counted separately? Give your answer as an integer.

Numerical answer type, tolerance 0.5.

Answer: 4

The cation

CH X_{2} = CH - CH X^{+} - CH X_{3}

is delocalised with

+ CH X_{2} - CH = CH - CH X_{3}

, so water can bond at C3 or at C1. Attack at C3 gives but-3-en-2-ol, which has one stereocentre (R and S, 2 isomers). Attack at C1 gives but-2-en-1-ol, which can be E or Z (2 isomers). The total is

2 + 2 = 4

(checked by enumerating stereoisomers in Python).

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Answer: 4

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