Question:
Which of the following functional groups will show -R effect?
Which of the following functional groups will show -R effect?
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Groups with a double/triple bond to an electronegative atom (like -NO\(_2\), -CN, -CHO, -COOH) show -R and -I effects.
Updated On: Apr 24, 2026
- -OH
- -OCH\(_3\)
- -NH\(_2\)
- -NO\(_2\)
- -NHCOCH\(_3\)
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
-R effect (negative resonance effect) occurs when a group withdraws electrons from the rest of the molecule by resonance. This typically happens with groups that have a π bond or a lone pair that can delocalize into the ring, but with an electronegative atom. More precisely, -R groups are electron-withdrawing by resonance.
Step 2: Detailed Explanation:
• -OH, -OCH\(_3\), -NH\(_2\), -NHCOCH\(_3\): These groups have lone pairs of electrons that can be donated into the aromatic ring. They show +R effect (electron-donating by resonance).
• -NO\(_2\): The nitro group has a π bond. The electronegative oxygen atoms withdraw electron density from the ring through resonance (the π electrons of the N=O bond can delocalize into the ring, creating a positive charge on the nitrogen and pulling electrons away). This is a strong -R effect.
Step 3: Final Answer:
The -NO\(_2\) group shows a -R effect.
-R effect (negative resonance effect) occurs when a group withdraws electrons from the rest of the molecule by resonance. This typically happens with groups that have a π bond or a lone pair that can delocalize into the ring, but with an electronegative atom. More precisely, -R groups are electron-withdrawing by resonance.
Step 2: Detailed Explanation:
• -OH, -OCH\(_3\), -NH\(_2\), -NHCOCH\(_3\): These groups have lone pairs of electrons that can be donated into the aromatic ring. They show +R effect (electron-donating by resonance).
• -NO\(_2\): The nitro group has a π bond. The electronegative oxygen atoms withdraw electron density from the ring through resonance (the π electrons of the N=O bond can delocalize into the ring, creating a positive charge on the nitrogen and pulling electrons away). This is a strong -R effect.
Step 3: Final Answer:
The -NO\(_2\) group shows a -R effect.
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