In the study of electrophilic aromatic substitution, the kinetic isotope effect () for the nitration of benzene () and hexadeuterobenzene () is observed to be approximately . What does this experiment

Question

In the study of electrophilic aromatic substitution, the kinetic isotope effect ($k_H / k_D$) for the nitration of benzene ($C_6H_6$) and hexadeuterobenzene ($C_6D_6$) is observed to be approximately $1$. What does this experimental observation conclusively prove about the mechanism?

Prashant Kotian · Accepted Answer

Correct answer: B. A primary kinetic isotope effect of indicates that the bond is not breaking during the slow, rate-determining step. In most EAS reactions, including nitration, the first step (formation of the arenium ion) is the slow, rate-determining step, while the second step (proton loss) is fast.

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