How does the Lucas test tell primary, secondary and tertiary alcohols apart?
The Lucas reagent (conc.
The Lucas reagent (conc. HCl + ZnCl₂) converts alcohols to alkyl chlorides, which show up as cloudiness. The rate depends on carbocation stability: a tertiary alcohol forms a stable 3° carbocation and turns cloudy at once; a secondary alcohol takes a few minutes; a primary alcohol barely reacts at room temperature. So the speed of turbidity reveals the class of alcohol.
Key point
Lucas test cloudiness is instant for 3°, slow for 2°, negligible for 1° (carbocation stability order).
Common mistake
expecting all alcohols to react at the same rate.
Memory tip
faster turbidity = more stable carbocation = more substituted alcohol.
Tap to watch or see it right here — the app stays open (it only opens a quick search if nothing embeddable is found).