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Lucas test (ZnCl2 + conc. HCl) gives immediate turbidity for which type of alcohol?

1. Primary alcohol (1°-R-OH)
2. Secondary alcohol (2°-R-OH)
3. Tertiary alcohol (3°-R-OH)
4. All types of alcohols

Correct answer: Tertiary alcohol (3°-R-OH)

Solution

Lucas test uses anhydrous ZnCl2 + concentrated HCl. The alcohol undergoes SN1 substitution to form an alkyl chloride (which is insoluble in the reagent, causing turbidity). The rate depends on carbocation stability. Tertiary alcohols form stable 3° carbocations instantly → immediate turbidity. Secondary alcohols react within ~5 min (mild turbidity). Primary alcohols do not react at room temperature (require heat). So immediate turbidity = tertiary alcohol.

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