Question

The dehydration of 1$^\circ$, 2$^\circ$ and 3$^\circ$ alcohols follows the order :

• A. 2$^\circ$ > 1$^\circ$ > 3$^\circ$
• B. 3$^\circ$ > 2$^\circ$ > 1$^\circ$
• C. 1$^\circ$ > 2$^\circ$ > 3$^\circ$
• D. 1$^\circ$ > 3$^\circ$ > 2$^\circ$

Hint:

Whenever dehydration proceeds through carbocation formation, remember: more stable carbocation means faster dehydration.

Answer 1

The Correct Option is B

Concept: Dehydration of alcohols occurs in acidic medium and proceeds through carbocation formation in most cases. The rate depends upon stability of carbocation formed.

Step 1: Carbocation stability order. \[ 3^\circ \gt 2^\circ \gt 1^\circ \] because alkyl groups stabilize positive charge through hyperconjugation and inductive effect.

Step 2: Relating carbocation stability to dehydration. More stable carbocation forms more easily. Hence dehydration occurs more readily. \[ 3^\circ \text{ alcohol} \] dehydrates fastest. \[ 1^\circ \text{ alcohol} \] dehydrates slowest.

Step 3: Final order. \[ \boxed{3^\circ \gt 2^\circ \gt 1^\circ} \] Hence option (B) is correct.