JEE Main 2021 · 24 Feb · Shift 1 · Chemistry Q43

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ChemistrySingle correct+4 / -1Question 43 of 90

The product formed in the first step of the reaction of $\mathrm{CH_3{-}CH_2{-}CHBr{-}CH_2{-}CHBr{-}CH_3}$ with excess Mg/Et $_2$ O (Et = C $_2$ H $_5$ ) is :

Reactant: 3,5-dibromohexane, CH3CH2-CHBr-CH2-CHBr-CH3.

A dimer: two C6 chains joined at the former C-Br carbons

Option A: two hexane chains joined between the former bromine-bearing carbons.

1-Ethyl-2-methylcyclopropane

Option B: a cyclopropane ring carrying an ethyl and a methyl group on adjacent carbons.

(no structure printed for this option)

The bis-Grignard reagent CH3CH2CH(MgBr)CH2CH(MgBr)CH3

Option D: CH3CH2CH(MgBr)CH2CH(MgBr)CH3, the bis-Grignard reagent.

Answer and worked solution

Official answer: D

Excess Mg turns each C-Br into C-MgBr; the 1,3 positions are too far apart for ring closure in the first step, so the bis-Grignard forms.

(D)

Topics:Polyhalogen compounds

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JEE Main 2021 · 24 Feb · Shift 1, Chemistry question 43