See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Solution: Thermal Decomposition of a Dihydroxy Acid **Structure of Starting Material:** The reactant is: $RCH(OH)-CH(OH)-C(=O)OH$ (a dihydroxy carboxylic acid or vicinal diol acid) **Reaction Mechanism (Heat, $\Delta$):** When heated, this molecule undergoes **intramolecular condensation** through the following steps: 1. **Nucleophilic attack:** The hydroxyl group on the central carbon attacks the carboxyl carbon ($C=O$) 2. **Water elimination:** A molecule of $H_2O$ is eliminated 3. **Ring formation:** A five-membered ring (dioxolane) forms with the carbonyl becoming part of the ring **Product Formation:** $$RCH-CH_2 \text{ with a dioxolane ring (5-membered ring containing two O atoms)}$$ This creates a **five-membered cyclic carbonate/dioxolane** structure as shown in option (A): the ring contains two oxygen atoms bonded to carbons, forming a stable cyclic ether-like system. **Why other options are wrong:** - **(B):** Forms a 6-membered ring (less favorable for 5-membered diol spacing) - **(C):** Glyoxal formation doesn't occur under these mild conditions - **(D):** Clearly incorrect **Answer: (A)** — Intramolecular cyclization produces a 5-membered dioxolane ring.