Question

From the following, identify the groups that exhibit negative resonance (-R) effect when attached to a conjugated system: \[ \text{Formyl (A), Amino (B), Alkoxy (C), Cyano (D), Nitro (E)} \]

• A. \( A, C, E \) only
• B. \( B, C, D \) only
• C. \( A, D, E \) only
• D. \( B, D, E \) only

Hint:

The -R effect is exhibited by electron-withdrawing groups containing double/triple bonds or strongly electronegative elements.

Answer 1

The Correct Option is C

Step 1: Understanding the -R effect. Groups that withdraw electron density from a conjugated system by resonance show a negative resonance effect (-R). Such groups contain strongly electronegative elements or multiple bonds adjacent to the system. 

Step 2: Identifying the correct groups.
- Formyl (-CHO), Cyano (-CN), and Nitro (-NO\(_2\)) groups exhibit the -R effect.
- Alkoxy (-OR) and Amino (-NH\(_2\)) groups show a positive resonance effect (+R). 
Thus, the correct answer is \( A, D, E \).