Question

Find out the correct statement from the options given below for the above 2 reactions.

• A. Reaction (I) is of 1^st order and reaction (II) is of 2^nd order
• B. Reaction (I) and (II) both are 2^nd order
• C. Reaction (I) is of 1^st order and reaction (II) is of 1^st order
• D. Reaction (I) is of 2^nd order and reaction (II) is of 1^st order

Hint:

Remember that electron-donating groups (like -OCH3) increase the nucleophilicity of the aromatic ring, leading to a first-order mechanism, while electron-withdrawing groups (like -NO2) decrease the nucleophilicity, making the reaction mechanism slower.

Answer 1

The Correct Option is C

- In the reaction involving an electron-donating group like $-OCH_3$, the electron density on the benzene ring is increased, leading to a faster nucleophilic attack. This makes the mechanism of reaction (I) 1^st order, as the rate depends on the concentration of the nucleophile only.

In the reaction involving an electron-withdrawing group like $-NO_2$, the electron density on the benzene ring is decreased, which slows down the nucleophilic substitution and typically follows a 2^ndorder mechanism, where both the nucleophile and the substrate are involved in the rate-determining step. However, reaction (II) involves a 1^st order mechanism because the presence of $-NO_2$ only partially influences the overall rate, which results in an overall first-order reaction. 
Thus, the correct answer is (3): Reaction (I) is of 1^st order and reaction (II) is of 1^st order.