Question

Which one of the following alcohols reacts instantaneously with Lucas reagent?

• A. \(\text{CH}_{3}-\text{CH}(\text{CH}_{3})-\text{CH}_{2}\text{OH}\)
• B. \(\text{CH}_{3}-\text{C}(\text{CH}_{3})(\text{OH})-\text{CH}_{3}\)
• C. \(\text{CH}_{3}-\text{CH}_{2}-\text{CH}_{2}-\text{CH}_{2}\text{OH}\)
• D. \(\text{CH}_{3}-\text{CH}_{2}-\text{CH}(\text{OH})-\text{CH}_{3}\)
• E.

Hint:

Identify the degree of the alcohol by counting the carbons attached to the C-OH carbon.
Instant turbidity = \(3^{\circ}\) Alcohol.
Delayed turbidity = \(2^{\circ}\) Alcohol.
No reaction = \(1^{\circ}\) Alcohol.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The Lucas test (conc. \(\text{HCl} + \text{anhyd. ZnCl}_{2}\)) is used to distinguish between \(1^{\circ}\), \(2^{\circ}\), and \(3^{\circ}\) alcohols.
The speed of reaction depends on the stability of the carbocation intermediate.

Step 2: Detailed Explanation:
The reactivity order towards Lucas reagent is:
Tertiary (\(3^{\circ}\)) \(>\) Secondary (\(2^{\circ}\)) \(>\) Primary (\(1^{\circ}\)).
- Tertiary alcohols react instantaneously to produce turbidity (alkyl chloride).
- Secondary alcohols react within 5-10 minutes.
- Primary alcohols do not react at room temperature.
Analyzing the options:
(A) 2-methylpropan-1-ol: Primary alcohol.
(B) 2-methylpropan-2-ol (tert-butyl alcohol): Tertiary alcohol.
(C) Butan-1-ol: Primary alcohol.
(D) Butan-2-ol: Secondary alcohol.
Since option (B) is a tertiary alcohol, it reacts immediately.

Step 3: Final Answer:
The alcohol that reacts instantaneously is 2-methylpropan-2-ol.