Question

An unknown compound decolorizes bromine in carbon tetrachloride, and it undergoes catalytic reduction to give decalin. When treated with warm, concentrated potassium permanganate, this compound gives cis-cyclohexane-1,2-dicarboxylic acid and oxalic acid. Propose a structure for the unknown compound.
Diagram illustrating the reaction of an unknown compound yielding decalin, cis-cyclohexane-1,2-dicarboxylic acid, and oxalic acid.

Diagram illustrating the reaction of an unknown compound yielding decalin, cis-cyclohexane-1,2-dicarboxylic acid, and oxalic acid.

Accepted Answer

Step 1: Analyze the reaction with bromine in carbon tetrachloride. The unknown compound decolorizes bromine, indicating the presence of a double bond or unsaturation in the molecule. This suggests that the compound is an alkene or contains an unsaturated ring system. Step 2: Examine the catalytic reduction reaction. The unknown compound undergoes catalytic hydrogenation (H₂, Pt) to form decalin, which is a bicyclic saturated hydrocarbon. This implies that the unknown compound is a bicyclic structure with unsaturation that can be reduced to decalin. Step 3: Consider the oxidation reaction with warm, concentrated potassium permanganate (KMnO₄). The reaction produces cis-cyclohexane-1,2-dicarboxylic acid and oxalic acid. This indicates that the unknown compound contains a double bond in a position that allows cleavage and oxidation to form these products. The cis configuration of the dicarboxylic acid suggests that the double bond is part of a ring system. Step 4: Propose the structure based on the products. The formation of cis-cyclohexane-1,2-dicarboxylic acid suggests that the double bond is located in a cyclohexane ring, and the production of oxalic acid indicates cleavage of a second double bond outside the ring. This points to a bicyclic structure with one double bond in the cyclohexane ring and another double bond in the second ring. Step 5: Combine all observations to propose the structure. The unknown compound is likely bicyclo[4.4.1]undeca-1,3-diene, which contains two double bonds: one in the cyclohexane ring and one in the second ring. This structure satisfies the reactions observed and the products formed.

An unknown compound decolorizes bromine in carbon tetrachloride, and it undergoes catalytic reduction to give decalin. When treated with warm, concentrated potassium permanganate, this compound gives cis-cyclohexane-1,2-dicarboxylic acid and oxalic acid. Propose a structure for the unknown compound.

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Key Concepts

Electrophilic Addition Reactions

Catalytic Hydrogenation

Oxidative Cleavage