Question

Which of the following is correct with respect to $- I$ effect of the substituents ? $(R =$ alkyl $)$

• A. $- NR_2 > -OR > - F $
• B. $- NH_2 < - OR < - F $
• C. $-NH_2 > - OR > - F $
• D. $-NR_2 < - OR > - F $

Answer 1

The Correct Option is B

The given question assesses the understanding of the inductive effect, specifically the $-I$ (negative inductive) effect of different substituents. This effect refers to the electron-withdrawing nature of groups when attached to a carbon atom, influencing the electron density of the molecule.

In the inductive effect, the $-I$ effect describes the tendency of a substituent to attract electrons towards itself, reducing the electron density on the atom it is attached to. A stronger $-I$ effect corresponds to a greater electron-withdrawing capability.

To understand the order of the $-I$ effect of the given substituents, we consider the following group characteristics:

1. $-NH_2$: The amino group has a relatively weak electron-withdrawing effect due to nitrogen's lone pair donation capability.
2. $-OR$: Oxygen is more electronegative than nitrogen, and the alkoxy group has a moderate electron-withdrawing effect.
3. $-F$: Fluorine is highly electronegative and strongly attracts electrons, making it one of the strongest electron-withdrawing groups by the inductive effect.

From the explanation above, the correct order of the $-I$ effect for the substituents is $-NH_2 < - OR < - F$, indicating that fluorine has the highest electron-withdrawing capability, followed by the alkoxy group, then the amino group.

Hence, the correct answer is the option: $- NH_2 < - OR < - F $.