See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Analysis of Acid Strength Among Given Compounds **Identify the compounds:** - (A) $HC \equiv CH$ (acetylene) - (B) $C_6H_6$ (benzene) - (C) $C_2H_6$ (ethane) - (D) $CH_3OH$ (methanol) **Key principle:** Acid strength depends on the stability of the conjugate base after H⁺ loss. **Step 1: Determine conjugate bases** - (A) $HC \equiv CH \rightarrow C \equiv C^-$ (acetylide anion) - (B) $C_6H_6 \rightarrow C_6H_5^-$ (phenyl anion) - (C) $C_2H_6 \rightarrow C_2H_5^-$ (ethyl anion) - (D) $CH_3OH \rightarrow CH_3O^-$ (methoxide anion) **Step 2: Assess conjugate base stability using hybridization** The negative charge is best stabilized on the carbon with highest $s$-character: - Acetylene ($sp$ hybridized): **50% s-character** ✓ Most stable - Benzene ($sp^2$ hybridized): 33% s-character - Ethane ($sp^3$ hybridized): 25% s-character - Methanol: Charge on oxygen (less electronegative than C for stabilization in this context) **Step 3: Conclude** $sp$ hybridization provides maximum $s$-character, making the acetylide anion most stable. Therefore, acetylene is the strongest acid. **Answer: (A) $HC \equiv CH$** with $pK_a \approx 25$