JEE Main · 2005 · 08 May 2005 · Offline · Hydrocarbons

2 methylbutane on reacting with bromine in the presence of sunlight gives mainly

(A)1 - bromo -2 - methylbutane
(B)2 - bromo -2 - methylbutane✓ Correct
(C)2 - bromo -3 - methylbutane
(D)1 - bromo -3 - methylbutane

Answer: (B)

Solution

Photochemical bromination is highly selective and goes for the most stable radical, which means the most substituted carbon. In 2-methylbutane that is the tertiary carbon at position 2, whose radical is steadied by three neighbouring alkyl groups; bromine's gentle, discriminating nature makes it strongly prefer this site over the primary and secondary positions. Abstracting the tertiary hydrogen and capping it with bromine gives mainly 2-bromo-2-methylbutane.

JEE Main · 2005 · 08 May 2005 · Offline · Single correct option

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