Question

Which among the following shows -R effect?

• A. -NO\(_2\)
• B. -NH\(_2\)
• C. -NHCOCH\(_3\)
• D. -OCH\(_3\)

Hint:

To identify the -R effect, look for groups with high electronegativity or those capable of delocalizing electrons through resonance. These groups withdraw electron density from the rest of the molecule.

Answer 1

The Correct Option is A

The -R effect (resonance withdrawing effect) refers to the ability of a substituent to withdraw electron density from a molecule via resonance. This typically occurs when the substituent has a lone pair of electrons or is highly electronegative, leading to the withdrawal of electron density from the rest of the molecule. - -NO\(_2\) (nitro group) is a strong electron-withdrawing group via resonance, making it exhibit the -R effect. The nitro group can pull electron density through the conjugated π-system, making it a powerful electron-withdrawing group. - -NH\(_2\) (amine group) is an electron-donating group, and it exhibits the +M effect (resonance donating effect). It does not withdraw electrons but donates them through its lone pair, making it the opposite of the -R effect. - -NHCOCH\(_3\) (acetamido group) is also an electron-withdrawing group due to the carbonyl group, but it operates through both -I (inductive) and -M (resonance) effects. However, it does not show the -R effect as strongly as the nitro group. - -OCH\(_3\) (methoxy group) is an electron-donating group via resonance (+M effect), and it does not show the -R effect. Thus, the correct answer is -NO\(_2\), as it exhibits the -R effect.