See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 - Understand the oxidative cleavage by KMnO4: KMnO4 under vigorous conditions cleaves carbon-carbon double bonds. Each double bond in an alkene is cleaved to give carboxylic acids (for internal carbons) or CO2 (for terminal carbons). Cyclic alkenes give dicarboxylic acids from one double bond cleavage. Step 2 - Analyze the products: The products are cyclohexane-1,2-dicarboxylic acid and oxalic acid (HOOC-COOH). Oxalic acid (two carbons, two carboxylic acids) comes from cleavage of a C=C double bond where both carbons each bear one additional carbon chain. Specifically, oxalic acid results from cleavage of a double bond where each carbon of the double bond is connected to a -COOH group - meaning each double-bond carbon was connected to one other carbon that became COOH. Step 3 - Work backward: Cyclohexane-1,2-dicarboxylic acid has a cyclohexane ring with COOH at C1 and C2. These COOH groups came from oxidation of double bonds. The two carbons bearing COOH in the product were originally connected by a double bond or were adjacent to double bonds. Since KMnO4 cleaves C=C, the C1-COOH and C2-COOH of the cyclohexane came from a double bond connecting C1 and C2 to another fragment. The oxalic acid (2 carbons) came from a two-carbon fragment that was doubly connected - i.e., a double bond between two carbons each of which was also bonded to C1 and C2 of the cyclohexane. Step 4 - Identify the structure: If compound A has a cyclohexane ring fused to a ring containing a C=C double bond, where the double bond carbons are directly attached to C1 and C2 of the cyclohexane, then KMnO4 cleavage of that double bond gives cyclohexane-1,2-dicarboxylic acid + a two-carbon diacid (oxalic acid). This means A has a cyclohexane ring fused with a four-membered portion containing one double bond - but more precisely, A is a bicyclic compound where a cyclohexane is fused to a ring containing one C=C. Option (b) shows 1,2-dihydronaphthalene: a naphthalene system where one ring is a cyclohexene (partially saturated), with the double bond in the non-aromatic ring. In 1,2-dihydronaphthalene, the non-aromatic ring contains one double bond between C3 and C4 (conjugated with the aromatic ring). KMnO4 oxidation cleaves the isolated/exocyclic double bond and oxidizes the aromatic ring portion. Actually, re-examining: option (b) is a structure where a six-membered ring with one double bond is fused to another six-membered ring with one double bond (not fully aromatic). The cleavage of the double bond between the two carbons shared or adjacent gives the cyclohexane-1,2-dicarboxylic acid from one ring and oxalic acid from the two-carbon bridge. The structure in option (b) - 1,2-dihydronaphthalene - upon KMnO4 oxidation cleaves the C=C in the dihydro ring, and further oxidizes to give cyclohexane-1,2-dicarboxylic acid and oxalic acid, consistent with the products shown. Step 5 - Eliminate other options: (a) has two double bonds or different connectivity giving different products; (c) naphthalene fused rings would give aromatic oxidation products; (d) decalin with one double bond at a different position would give different chain lengths. Only option (b) gives exactly cyclohexane-1,2-dicarboxylic acid and oxalic acid upon KMnO4 oxidative cleavage. Therefore, the correct answer is B.