What is the correct order of reactivity towards sulphonation or iodination?

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$C_{6} H_{6} = C_{6} D_{6} > C_{6} T_{6}$

$C_{6} H_{6} = C_{6} D_{6} = C_{6} T_{6}$

$C_{6} H_{6} > C_{6} D_{6} > C_{6} T_{6}$

$C_{6} H_{6} > C_{6} D_{6} = C_{6} T_{6}$

answer is B.

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Detailed Solution

The correct order of the rate of reaction of C₆H₆, C₆D₆ and C₆T₆ towards sulphonation is C₆H₆>C₆D₆>C₆T₆.
As the hydrogen atom of benzene is successively substituted with deuterium and tritium, the rate of the electrophilic aromatic substitution decreases.
Concentrated sulphuric acid releases a molecule of SO₃.
The electrophile attacks the benzene ring to form a sigma complex.
The abstraction of H₊ is the rate determining step.
The bond strength increases in the order C−H < C−D < C−T.
Hence, the rate of the reaction decreases in the order C₆H₆>C₆D₆>C₆T₆.

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