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Question #44626

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The Question

Consider the dehydration of 3,3-dimethylbutan-2-ol under two different sets of conditions:

Condition I: Treatment with $\ce{POCl3}$ in pyridine at $0^\circ\text{C}$ to give major product $P$ . Condition II: Heating with $85\% \ \ce{H3PO4}$ at $150^\circ\text{C}$ to give major product $Q$ .

Identify the major products $P$ and $Q$ .

Options

A.
$P$ = $\ce{CH2=CH-C(CH3)3}$ ; $Q$ = $\ce{(CH3)2C=C(CH3)2}$
B.
$P$ = $\ce{(CH3)2C=C(CH3)2}$ ; $Q$ = $\ce{CH2=CH-C(CH3)3}$
C.
$P$ = $\ce{(CH3)2C=C(CH3)2}$ ; $Q$ = $\ce{(CH3)2C=C(CH3)2}$
D.
$P$ = $\ce{CH2=CH-C(CH3)3}$ ; $Q$ = $\ce{CH2=C(CH3)-CH(CH3)2}$

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

E2 Regioselectivity (Saytzeff vs Hoffmann)|SN1 Carbocation Rearrangement|E1/E2 Solvent and Base Effects

Why This Question Is Tricky

Common Mistakes

This problem tests the critical distinction between concerted (E2) and step-wise (E1) elimination pathways.

The 'Chemical Exception' trap exploits the student's reflex to always rearrange highly branched substrates to the most stable alkene.

However, under E2 conditions ( $\ce{POCl3}$ /pyridine), the lack of a carbocation intermediate and the absence of $\beta$ -hydrogens on the quaternary carbon strictly force the formation of the less substituted terminal alkene.

Failing to recognize the mechanistic divergence leads to incorrect thermodynamic assumptions.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Haloalkanes and Haloarenes - Class 12
Concept	E2 Regioselectivity (Saytzeff vs Hoffmann)
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free