The treatment of $\mathrm{CH}_{3} \mathrm{MgX}$ with $\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{C}-\mathrm{H}$ produces

(A) $\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2}$

(B) $\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{C}-\mathrm{CH}_{3}$

JEE Main · 2008 · 27 Apr 2008 · Offline · Haloalkanes and Haloarenes

The treatment of

CH_{3} MgX

with

CH_{3} C \equiv C - H

produces

(A) $CH_{3} - CH = CH_{2}$
(B) $CH_{3} C \equiv C - CH_{3}$
(C)(see structure)
(D) $CH_{4}$ ✓ Correct

Answer: (D)

Solution

A Grignard reagent is a powerful base, and a terminal alkyne carries a genuinely acidic hydrogen on its

s p

-carbon. When

C H_{3} MgX

meets

C H_{3} C \equiv CH

it simply removes that acidic hydrogen, so the methyl group leaves as methane while the alkyne is converted to its magnesium acetylide. The hydrocarbon product collected is therefore methane,

C H_{4}

JEE Main · 2008 · 27 Apr 2008 · Offline · Single correct option

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