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KEAM 2011 Physics and Chemistry Paper

Question : 83 of 120

Marks: +1, -0

The stablest radical among the following is

$\mathrm{C}_6\mathrm{H}_5\mathrm{CH}_2-\mathrm{CH}_2$
$\mathrm{CH}_3\mathrm{CH}_2$
$\mathrm{C}-6\mathrm{H}_5-\mathrm{CH}-\mathrm{CH}_3$
$\mathrm{CH}_3-\mathrm{CH}-\mathrm{CH}_3$
$\mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2$

Solution:

The benzylic free radicals are more stable than alkyl free radicals because of the delocalisation of odd or unpaired electron on the benzene ring. Further, secondary free radical is more stable than primary free radical. Therefore

\mathrm{C}_6\mathrm{H}_5-\overset{\bullet}{\mathrm{C}}\mathrm{H}-\mathrm{CH}_3

is more stable than

\mathrm{C}_6\mathrm{H}_5-\mathrm{CH}_2-\overset{\bullet}{\mathrm{C}}\mathrm{H}_2

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