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Question #45038

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The Question

Mixed anhydride \ce{X} is synthesized by the condensation of acetic acid and trifluoroacetic acid. Let $O_{Ac}$ and $O_{TFA}$ be the formal IUPAC oxidation states of the carbonyl carbons of the acetate and trifluoroacetate moieties in \ce{X}, respectively.

\ce{X} is subjected to reduction under two different conditions: Condition 1: Treatment with excess \ce{NaBH4} in THF at $0 ^\circ\text{C}$ , followed by aqueous acidic workup, yields alcohol \ce{P} as the major organic reduction product. Condition 2: Treatment with excess L-Selectride (\ce{Li(sec-Bu)3BH}) in THF at $-78 ^\circ\text{C}$ , followed by aqueous acidic workup, yields alcohol \ce{Q} as the major organic reduction product.

Identify the correct set of $(O_{Ac}, O_{TFA})$ , \ce{P}, and \ce{Q}.

Options

A.
$(+3, +3)$ , \ce{P} = \ce{CF3CH2OH}, \ce{Q} = \ce{CH3CH2OH}
B.
$(+3, +4)$ , \ce{P} = \ce{CH3CH2OH}, \ce{Q} = \ce{CF3CH2OH}
C.
$(+3, +3)$ , \ce{P} = \ce{CH3CH2OH}, \ce{Q} = \ce{CF3CH2OH}
D.
$(+3, +4)$ , \ce{P} = \ce{CF3CH2OH}, \ce{Q} = \ce{CH3CH2OH}

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Fractional Oxidation State Misconception|Oxidation State Traps|Reduction Selectivity (Hydrides)

Why This Question Is Tricky

Common Mistakes

This problem tests the student's ability to decouple formal Oxidation State from fractional positive charge ( $\delta+$ ), and to evaluate competing steric and electronic effects in hydride reductions.

The 'Oxidation State Trap' forces students to realize that IUPAC rules dictate homolytic cleavage for C-C bonds regardless of extreme inductive effects, keeping both carbonyl carbons at +3.

The 'Reaction Blueprint' pits a small hydride (\ce{NaBH4}) against a massive hydride (L-Selectride).

Students often assume a uniform reactivity based on the anhydride functional group, but must recognize that \ce{NaBH4} follows electronic control (attacking the highly electrophilic but hindered \ce{CF3-CO} site), while L-Selectride follows strict steric control (attacking the less hindered \ce{CH3-CO} site).

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Redox Reactions - Class 11 Part 2
Concept	Fractional Oxidation State Misconception
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free