Before You Begin

Question #45051

Difficulty: 8/10 | 🟢 Free

The Question

Consider the reaction of 1,1,1-trifluorobut-3-yn-2-one with exactly one equivalent of methylmagnesium bromide ( $\ce{CH3MgBr}$ ) in dry THF at $195\text{ K}$ . The reaction mixture is subsequently quenched with an excess of heavy water ( $\ce{D2O}$ ). What is the major organic product formed?

Options

A.
$DC \equiv C-C(=O)-CF_3$
B.
$HC \equiv C-C(OD)(CH_3)-CF_3$
C.
$DC \equiv C-C(OD)(CH_3)-CF_3$
D.
$CH_3-C \equiv C-C(=O)-CF_3$

Check Your Answer

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

Inductive Effect (I-Effect)|Grignard Reagent Sensitivity|Alkynes Terminal Acidity

Why This Question Is Tricky

Common Mistakes

This question tests the classic 'Acid-Base vs.

Nucleophilic Addition' paradigm, specifically exploiting the student's recognition of the Inductive Effect (-I).

The trap is set by the trifluoromethyl group: students will correctly deduce that the -CF3 group makes the carbonyl carbon exceptionally electrophilic, leading them to predict nucleophilic addition (Option B).

However, they overlook the 'Hidden Variable'—the same -I and -M effects drastically lower the pKa of the terminal alkyne proton.

Because proton transfer is diffusion-controlled, the Grignard reagent will invariably act as a base first, quenching the reaction before any nucleophilic attack can occur.

The strict 1:1 stoichiometry ensures no secondary addition takes place.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Organic Chemistry – Some Basic Principles and Techniques - Class 11 Part 2
Concept	Inductive Effect (I-Effect)
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free