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Question #43968

Difficulty: 8/10 | 🟢 Free

The Question

Consider the following reaction sequence:

$\ce{CH3-CO-CH3} \xrightarrow[\text{THF, } -78^\circ\text{C}]{\text{LDA (1 eq.)}} \text{X}$

$\text{X} \xrightarrow[\text{2. } \ce{H3O^+}]{\text{1. } \ce{(CH3)3C-CHO}} \text{P}$

$\text{P} \xrightarrow[\text{2. } \ce{H3O^+}]{\text{1. } \ce{LiAlH4}, \text{ dry ether}} \text{Q}$

$\text{Q} \xrightarrow[\text{298 K}]{\ce{HIO4} \text{ (aq)}} \text{R}$

Identify the structure of the final major product R.

Options

A.
$\ce{(CH3)3C-CH(OH)-CH2-CH(OH)-CH3}$
B.
$\ce{(CH3)3C-CHO} + \ce{CH3-CHO} + \ce{HCHO}$
C.
$\ce{(CH3)3C-CH(OH)-CH2-CO-CH3}$
D.
$\ce{(CH3)3C-CH=CH-CH(OH)-CH3}$

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

Aldol Condensation Directionality|Glycol Periodic Acid Cleavage|Reduction Selectivity (Hydrides)

Why This Question Is Tricky

Common Mistakes

The question tests the student's ability to track functional group transformations through a multi-step synthesis (Directed Aldol $\rightarrow$ Hydride Reduction) and evaluates their understanding of the strict structural prerequisites for oxidative cleavage.

The 'Chemical Exception' being tested is the inertness of 1,3-diols towards $\ce{HIO4}$ .

Students often fall into the trap of assuming that any polyol will undergo cleavage, failing to recognize that the 1,3-relationship generated by the Aldol-reduction sequence prevents the formation of the requisite 5-membered cyclic periodate intermediate.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Aldehydes, Ketones, and Carboxylic Acids - Class 12
Concept	Aldol Condensation Directionality
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free