See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Steric Inhibition of Resonance - Solution **Concept:** Steric inhibition of resonance occurs when bulky groups physically block the coplanarity needed for a lone pair to delocalize into an aromatic ring's π-system. **Analysis of each option:** **(A)** $N(CH_3)_2$ directly attached to benzene with **two ortho methyl groups** - The two ortho methyls create severe steric crowding - They force the $N(CH_3)_2$ group out of the ring plane - Lone pair on $N$ cannot overlap with aromatic π-system - **Resonance is inhibited** ✓ **(B)** $N(CH_3)_2$ at meta position with ortho methyls on ring - Meta methyls don't block resonance (lone pair can still delocalize) - Less steric hindrance to planarity **(C)** $N(CH_3)_2$ at para position with t-Bu group - Para substitution doesn't cause ortho steric clash with $N(CH_3)_2$ - Resonance proceeds normally **(D)** $N(CH_3)_2$ at meta position with **two t-Bu groups** - Though bulky, the $N(CH_3)_2$ is meta to both groups - Steric blocking is minimal; resonance still possible **Why (A) is correct:** The ortho-disubstituted methyls directly adjacent to the $N(CH_3)_2$ group create maximum steric hindrance, forcing the nitrogen's lone pair perpendicular to the ring plane and preventing resonance donation to the aromatic system.