Question

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

• A. – NH₂ < – OR < – F
• B. – NH₂ > – OR > – F
• C. – NR₂ < – OR < – F
• D. – NR₂ > – OR > – F

Answer 1

The Correct Option is A

 The question asks us to determine the order of the –I effect (inductive effect) of different substituents compared to an alkyl group (R). The inductive effect is an electronic effect due to the polarization of σ bonds within a molecule. Substituents or functional groups can either have a +I effect, which is electron-donating, or a –I effect, which is electron-withdrawing.

Let's analyze each substituent provided in the options to understand their –I effect.

1. –NH₂ (Amino group): The amino group is known to be less effective in withdrawing electrons compared to more electronegative atoms like fluorine. It tends to donate electrons due to resonance in specific contexts, but in the context of pure inductive effect comparison, it's a weaker –I group.
2. –OR (Alkoxy group): Alkoxy groups are more electronegative compared to amino groups due to the presence of an oxygen atom, making them moderate –I effect groups.
3. –F (Fluorine): Being one of the most electronegative elements, fluorine exerts a strong –I effect as it strongly withdraws electrons through the σ bond.

Based on the above analysis, we can conclude the correct order of –I effect strength as:

\(- \text{NH}_2 < - \text{OR} < - \text{F}\)

This order indicates that the fluorine atom has the strongest –I effect due to its high electronegativity, followed by the alkoxy group, and finally the amino group having the weakest –I effect among the given options.

Thus, the correct answer is: – NH₂ < – OR < – F