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Among the following alcohols, how many will produce an immediate white turbidity (precipitate) when treated with Lucas reagent (anhydrous ZnCl2 / conc. HCl) at room temperature? The compounds are: (i) 1-butanol, (ii) 2-butanol, (iii) 2-methyl-2-propanol (tert-butanol), (iv) benzyl alcohol.

1. 1
2. 2
3. 3
4. 4

Correct answer: 2

Solution

Lucas reagent (ZnCl2 / conc. HCl) converts alcohols to alkyl chlorides. Tertiary alcohols react immediately (stable carbocation) and benzylic alcohols react immediately (resonance-stabilised carbocation). Secondary alcohols react slowly (several minutes). Primary aliphatic alcohols essentially do not react at room temperature. So tert-butanol and benzyl alcohol give immediate turbidity -> 2 compounds.

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