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Question #44396

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The Question

Phenol is treated with $\ce{CHCl3}$ and aqueous $\ce{NaOH}$ at $340\text{ K}$ to form an intermediate mixture containing compound $\textbf{P}$ as the major organic species. Without isolating $\textbf{P}$ , an excess of acetone is added to the strongly basic reaction mixture and heated. Subsequent careful acidification of the mixture yields compound $\textbf{Q}$ as the major product.

Identify the IUPAC name and stereochemistry of compound $\textbf{Q}$ .

Options

A.
(3E)-4-(2-hydroxyphenyl)but-3-en-2-one
B.
(3E)-4-(4-hydroxyphenyl)but-3-en-2-one
C.
4-methylpent-3-en-2-one
D.
(1E,4E)-1,5-bis(2-hydroxyphenyl)penta-1,4-dien-3-one

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Explanation

How the Examiner Thinks

Mechanism_Trap

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Concepts Behind This Question

Reimer-Tiemann Reaction|Aldol Condensation Directionality|Alpha-Hydrogen Acidity

Why This Question Is Tricky

Common Mistakes

The 'Chemical Exception' being tested is the reactivity of the salicylaldehyde intermediate under strongly basic conditions.

Students often mistakenly assume that the conversion of the phenolic -OH to a phenoxide ion ( $\ce{O-}$ ) strongly deactivates the adjacent aldehyde towards nucleophilic attack via resonance (+R effect).

This leads to the incorrect prediction that the self-aldol condensation of acetone (yielding mesityl oxide) will dominate.

The framework forces the student to recognize that the aldehyde remains the superior electrophile (Claisen-Schmidt condensation) and that the thermodynamic driving force of the highly conjugated cross-aldol product overcomes the phenoxide's deactivation.

Furthermore, it tests the regioselectivity of the Reimer-Tiemann reaction (ortho vs. para) and the stoichiometric control (excess acetone) preventing the double cross-aldol product.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Alcohols, Phenols, and Ethers - Class 12
Concept	Reimer-Tiemann Reaction
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free