See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Step 1 - Concept: Ring strain arises primarily from angle strain (deviation of bond angles from ideal values) and, to a lesser extent, torsional strain. Smaller rings have greater angle strain because the interior angles of the ring deviate more from the ideal sp3 (~109.5°) or sp2 (~120°) bond angles. Step 2 - Ranking ring sizes by strain: Three-membered rings > four-membered rings > five-membered rings ≈ six-membered rings (nearly strain-free). Step 3 - Identify ring sizes: (a) delta-lactone is a six-membered ring — essentially strain-free (chair conformation available). (b) gamma-lactone is a five-membered ring — slightly strained but relatively stable; five-membered rings adopt envelope conformations with modest angle strain. (c) beta-lactone is a four-membered ring — highly strained due to severe angle strain (interior angles forced to ~90° vs. ideal ~109.5° for sp3 and ~120° for sp2 carbonyl carbon), making it the most reactive and strained among the options. (d) delta-lactam is a six-membered ring — essentially strain-free, similar to (a). Step 4 - Why other options fail: - Options (a) and (d) are six-membered rings with negligible ring strain. - Option (b) is a five-membered ring with low ring strain. - Only option (c), the four-membered beta-lactone, experiences significant angle strain. Step 5 - Conclusion: The beta-lactone (four-membered cyclic ester) in option (c) is the most highly strained ring among the choices given. Therefore, the correct answer is C.