JEE Main · 2019 · 10 Jan 2019 · Shift 1 · Hydrocarbons

Which hydrogen in compound(E) is easily replaceable during bromination reaction in presence of light?

(A)α - hydrogen✓ Correct
(B)γ - hydrogen
(C)δ - hydrogen
(D)β - hydrogen

Answer: (A)

Solution

Photochemical bromination removes whichever hydrogen leaves the most stable radical behind, since that is the easiest C-H bond to break homolytically. The hydrogen on the carbon next to the double bond gives an allylic radical whose unpaired electron is spread over the

π

system, and that resonance stabilisation makes it far easier to pull off than the others. So the

α

-hydrogen is the one most readily replaced.

JEE Main · 2019 · 10 Jan 2019 · Shift 1 · Single correct option

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