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Question #44368

Difficulty: 8/10 | 🟢 Free

The Question

Consider the following reaction sequence:

$\text{6-methylhept-5-en-2-one} \xrightarrow{\text{1. } \ce{NaBH4}, \text{ EtOH}, 298\text{ K}} \text{Intermediate A}$

$\text{Intermediate A} \xrightarrow{\text{2. } \ce{H2SO4} \text{ (aq, } 10\%), 298\text{ K}} \text{Major Product B}$

Identify the structure of the Major Product B.

Options

A.
6-methylheptane-2,6-diol
B.
2,2,6-trimethyltetrahydro-2H-pyran
C.
2-isopropyl-5-methyltetrahydrofuran
D.
6-methylhept-5-en-2-ol

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

Acid-Catalyzed Hydration Mechanism|Reduction Selectivity (Hydrides)

Why This Question Is Tricky

Common Mistakes

This problem tests the concept of chemoselectivity and the kinetic advantage of intramolecular reactions over intermolecular ones.

Students often fall into the trap of treating sequential reactions in isolation.

While Step 2 uses standard acid-catalyzed hydration conditions (dilute H2SO4), the presence of the newly formed secondary alcohol from Step 1 creates a competing internal nucleophile.

The 'Hidden Variable' is the entropic favorability of forming a stable 6-membered cyclic ether via a tertiary carbocation, which vastly outcompetes intermolecular attack by water to form the diol (Option A).

Option C traps students who erroneously prioritize 5-membered ring formation over carbocation stability (forming a secondary carbocation at C5).

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Alcohols, Phenols, and Ethers - Class 12
Concept	Acid-Catalyzed Hydration Mechanism
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free