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Question #44141

Difficulty: 8/10 | 🟢 Free

The Question

2,6-Dimethylbenzoic acid (A\mathbf{A}) and benzoic acid (B\mathbf{B}) are subjected to esterification studies. Under standard Fischer esterification conditions (excess \ce{EtOH}, catalytic \ce{H2SO4}, 298 K), A\mathbf{A} fails to react due to severe steric hindrance. To achieve the esterification of A\mathbf{A}, it is first dissolved in 100% \ce{H2SO4} to generate a reactive intermediate X\mathbf{X}, which is subsequently treated with cold ethanol. When A\mathbf{A} and B\mathbf{B} are dissolved in 100% \ce{H2SO4}, their cryoscopic van't Hoff factors are observed to be iAi_A and iBi_B, respectively. Identify the correct values of iAi_A and iBi_B, the hybridization of the electrophilic carbon in X\mathbf{X}, and the primary thermodynamic driving force for the formation of X\mathbf{X} over a standard protonated species.

Options

  • A.

    iA=4i_A = 4, iB=2i_B = 2, spsp, Relief of B-Strain

  • B.

    iA=2i_A = 2, iB=2i_B = 2, sp2sp^2, Hyperconjugation

  • C.

    iA=4i_A = 4, iB=3i_B = 3, sp2sp^2, Steric Inhibition of Resonance

  • D.

    iA=3i_A = 3, iB=2i_B = 2, spsp, Redox-neutral cyclization

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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

Electron Transfer Accounting|Nucleophilic Acyl Substitution|Esterification Reversibility|Steric Hindrance (B-Strain)

Why This Question Is Tricky

Common Mistakes

The question tests the 'Chemical Exception' of the ortho effect in esterification.

Students often blindly apply Fischer esterification kinetics and assume simple protonation (i=2i=2) for all carboxylic acids in sulfuric acid.

The hidden variable is the steric hindrance (B-Strain) that prevents the formation of the sp3sp^3 tetrahedral intermediate, forcing the molecule to undergo dehydration to a linear spsp hybridized acylium ion.

This changes the electron transfer accounting, resulting in an anomalous van't Hoff factor of 4 instead of 2.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterRedox Reactions - Class 11 Part 2
ConceptElectron Transfer Accounting
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree