Which of the following electrophilic aromatic substitution reactions exhibits a measurable kinetic isotope effect () because its energy barrier for reverting to reactants is comparable to the barrier

Question

Which of the following electrophilic aromatic substitution reactions exhibits a measurable kinetic isotope effect ($k_H/k_D > 1$) because its energy barrier for reverting to reactants is comparable to the barrier for proton loss?

Prashant Kotian · Accepted Answer

Correct answer: B. Sulfonation is highly reversible. The arenium intermediate can either revert to reactants or lose a proton with similar activation energies. Using heavier deuterium raises the barrier for the second step, slowing the forward reaction and producing an isotope effect.

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