Before You Begin

Question #45087

Difficulty: 8/10 | 🟢 Free

The Question

1-Hexyne on treatment with aqueous $\ce{H_2SO_4}$ in the presence of $\ce{HgSO_4}$ gives a major product $\ce{X}$ . Compound $\ce{X}$ is then subjected to the following reaction sequence:

$\ce{LDA}$ (1.05 eq.), $\ce{THF}$ , $-78^\circ\text{C}$
$\ce{PhCHO}$
$\ce{H_3O^+}$ , $\Delta$

Assuming ideal conditions, identify the major product $\ce{Y}$ formed at the end of the sequence.

Options

A.
(E)-1-phenylhept-1-en-3-one
B.
(E)-3-benzylidenehexan-2-one
C.
(E)-2-benzylidenehexanal
D.
(E)-1-phenylhept-2-en-1-one

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

Reaction Intermediates Stability|Alpha-Hydrogen Acidity|Aldol Condensation Directionality

Why This Question Is Tricky

Common Mistakes

The problem tests the student's mastery of regiocontrol in enolate chemistry.

The 'Hidden Variable' is the specific reagent condition ( $\ce{LDA}$ at $-78^\circ\text{C}$ ), which forces the reaction down a kinetic pathway.

Students often blindly apply Zaitsev's rule or assume thermodynamic stability dictates the major product, leading them to incorrectly choose the more substituted enolate (C3 attack).

By combining this with an initial alkyne hydration step, the question also verifies the student's understanding of Markovnikov regioselectivity, effectively punishing those who assume anti-Markovnikov hydration (which would lead to the aldehyde distractor).

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Organic Chemistry – Some Basic Principles and Techniques - Class 11 Part 2
Concept	Reaction Intermediates Stability
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free