Question

From the following list, identify the number of substituents which exert \(+R\) effect when present on benzene ring \[ -Cl,\quad -COCH_3,\quad -NHC_2H_5,\quad -OCH_3,\quad -NHCOCH_3,\quad -COOCH_3 \]

• A. 5
• B. 6
• C. 3
• D. 4

Hint:

Common \(+R\) groups: \[ -OH,\ -OR,\ -NH_2,\ -NHR,\ -NR_2,\ -Cl,\ -Br \] Common \(-R\) groups: \[ -CHO,\ -COR,\ -COOH,\ -COOR,\ -CN,\ -NO_2 \] Lone-pair-containing atoms attached directly to benzene usually show \(+R\) effect.

Answer 1

The Correct Option is D

Concept: Groups having a lone pair directly attached to the benzene ring can donate electron density through resonance and show \[ +R \; (\text{or } +M) \] effect. Groups containing a carbonyl group attached to the ring generally withdraw electrons by resonance and show \[ -R \; (\text{or } -M) \] effect.

Step 1: Examine each substituent. \[ -Cl \] Chlorine possesses lone pairs and donates electrons through resonance. \[ \boxed{+R} \] \[ -COCH_3 \] Carbonyl group withdraws electrons from the ring. \[ \boxed{-R} \] \[ -NHC_2H_5 \] Nitrogen has a lone pair available for resonance donation. \[ \boxed{+R} \] \[ -OCH_3 \] Oxygen donates its lone pair to the ring. \[ \boxed{+R} \] \[ -NHCOCH_3 \] Although the lone pair is partially involved with the carbonyl group, it can still donate electron density to the benzene ring. \[ \boxed{+R} \] \[ -COOCH_3 \] Ester carbonyl attached to the ring withdraws electrons by resonance. \[ \boxed{-R} \]

Step 2: Count the \(+R\) groups. \[ -Cl,\quad -NHC_2H_5,\quad -OCH_3,\quad -NHCOCH_3 \] Number of \(+R\) groups \[ =4. \]

Final Answer: \[ \boxed{4} \] \[ \boxed{\text{Answer = (D)}} \]