See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

## Solution: Arranging Compounds in Order of Decreasing Acidity **Key Principle:** The acidity of compounds containing $NO_2$ groups depends on: - Number of electron-withdrawing $NO_2$ groups (more $NO_2$ = more acidic) - Proximity of $NO_2$ to the acidic hydrogen (closer = more acidic due to greater stabilization of conjugate base) **Analysis of Each Compound:** **(1) $CH_3-NO_2$** (Nitromethane) - One $NO_2$ group directly attached to $CH_3$ - Moderately acidic (one activating group) **(2) $NO_2-CH_2-NO_2$** (Dinitromethane) - Two $NO_2$ groups on the same carbon - Highly acidic (two electron-withdrawing groups directly on acidic carbon) - Forms highly stabilized carbanion: $[NO_2-CH^-_-NO_2]$ **(3) $CH_3-CH_2-NO_2$** (Nitroethane) - One $NO_2$ group at distance (separated by $CH_2$) - Less acidic than (1) because $NO_2$ effect is attenuated over one carbon **(4) $NO_2-CH(-NO_2)_2$** (Trinitromethane) - Three $NO_2$ groups on one carbon - **Most acidic** (maximum electron withdrawal and conjugate base stabilization) **Order of Decreasing Acidity:** $$\boxed{(4) > (2) > (1) > (3)}$$ **Why (A) is correct:** Compound (4) with three $NO_2$ groups is most acidic; (2) with two proximal $NO_2$ groups is next; (1) with one $NO_2$ is more acidic than (3) where the $NO_2$ is farther from the acidic H.