See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Analysis of Acidity **Step 1: Identify the compounds** - (A) Cyclopropane ($C_3H_6$) — three-membered ring - (B) Cyclopentadiene ($C_5H_6$) — five-membered ring with one $C=C$ double bond - (C) Benzene ($C_6H_6$) — six-membered aromatic ring - (D) Propene ($CH_2=CH-CH_3$) — alkene **Step 2: Determine where acidic hydrogens are** - (B), (C), (D): These have normal $sp^2$ or $sp^3$ hybridized C-H bonds with typical acidity - (A): Has hydrogens on $sp^3$ carbons in a highly strained 3-membered ring **Step 3: Apply strain effect** Cyclopropane experiences significant ring strain (~27.5 kcal/mol). The three-membered ring geometry forces very small C-C-C angles (~60°), which: - Weakens C-H bonds - Makes electrons in C-H bonds less available to the carbon - The carbon becomes more electron-deficient and acidic - $pK_a$ of cyclopropane ≈ 46 (most acidic among these) **Step 4: Compare relative acidities** $$pK_a: \text{Cyclopropane}(46) < \text{Cyclopentadiene}(~16) < \text{Benzene}(43) < \text{Propene}(44)$$ **Answer: (A)** — Cyclopropane's ring strain makes its C-H bonds unusually acidic.