Assertion (A): Tertiary alcohols produce turbidity immediately with Lucas reagent (concentrated HCl and ZnCl2).
Reason (R): Tertiary carbocations are less stable and therefore harder to form than secondary and primary carbocations.
In the light of the above statements, choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) is true but (R) is false.
In the Lucas test, an alcohol reacts with concentrated HCl and ZnCl2 to give an alkyl chloride. The alcohol dissolves in the reagent, but the chloride does not, so the solution turns turbid. How soon the turbidity appears depends on how easily the alcohol forms the halide.
Assertion (A): Tertiary alcohols produce turbidity immediately with Lucas reagent (concentrated HCl and ZnCl2). — True. Tertiary alcohols form the chloride easily, so turbidity appears at once. Primary alcohols give no turbidity at room temperature, which is how the test tells the three classes apart.
Reason (R): Tertiary carbocations are less stable and therefore harder to form than secondary and primary carbocations. — False. The order is the reverse: tertiary carbocations are the most stable and are formed most easily. For the same reason tertiary alcohols are also the easiest to dehydrate.
NCERT (2026-27 edition):
7.4.4 Chemical Reactions – “The difference in reactivity of three classes of alcohols with HCl distinguishes them from one another (Lucas test). Alcohols are soluble in Lucas reagent (conc. HCl and ZnCl2) while their halides are immiscible and produce turbidity in solution. In case of tertiary alcohols, turbidity is produced immediately as they form the halides easily. Primary alcohols do not produce turbidity at room temperature.”
“Tertiary carbocations are more stable and therefore are easier to form than secondary and primary carbocations; tertiary alcohols are the easiest to dehydrate.”