See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Acidic Strength Order for Unsaturated Carboxylic Acids **Key Principle:** Acidity of carboxylic acids increases with electron-withdrawing effects near the carboxyl group. Unsaturation (double/triple bonds) withdraws electron density through inductive effects. ## Step-by-Step Analysis: **1) Propanoic acid: $CH_3CH_2COOH$** - Saturated alkyl chain attached to $-COOH$ - Weakest electron-withdrawing effect - **Least acidic** **2) Acrylic acid: $CH_2=CH-COOH$** - $sp^2$ carbon in C=C is more electronegative than $sp^3$ carbon - Double bond withdraws electron density inductively - **Moderately acidic** **3) Propiolic acid: $HC \equiv C-COOH$** - $sp$ carbon in $C \equiv C$ is **most electronegative** - Triple bond withdraws maximum electron density from the carboxyl group - This **strongly stabilizes the conjugate base** by delocalizing negative charge - **Most acidic** ## Trend: Electron-withdrawing power: $sp < sp^2 < sp^3$ $$CH_3CH_2COOH < CH_2=CH-COOH < HC\equiv C-COOH$$ **Answer: (D)** ✓