An unknown hydrocarbon A with the formula C6 H12 reacts with 1 molar equivalent of H2 over a pal

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An unknown hydrocarbon A with the formula C6 H12 reacts with...

An unknown hydrocarbon $A$ with the formula $\mathrm{C}_{6} \mathrm{H}_{12}$ reacts with 1 molar equivalent of $\mathrm{H}_{2}$ over a palladium catalyst. Hydrocarbon $\mathrm{A}$ also reacts with $\mathrm{OsO}_{4}$ to give diol $\mathrm{B}$. When oxidized with $\mathrm{KMnO}_{4}$ in acidic solution, A gives two fragments. One fragment is propanoic acid, $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H},$ and the other fragment is ketone $\mathrm{C}$. What are the structures of $\mathrm{A}, \mathrm{B},$ and C? Write all reactions, and show your reasoning.

Key Concepts

Structure Elucidation by Reaction Outcome Analysis

This key concept involves deducing the structure of an unknown organic molecule from the products obtained in its chemical reactions. In the problem, the fact that one oxidation fragment is propanoic acid and the other is a ketone (which must be derived from a more highly substituted carbon) allows one to infer the placement of substituents around the original double bond. By accounting for the number of carbons and the oxidation behavior of each double?bonded carbon, one can reconstruct the structure of the starting hydrocarbon.

Syn Dihydroxylation with OsO4

Osmium tetroxide (OsO4) reacts with alkenes to add two hydroxyl groups across the double bond via a syn addition mechanism. The reaction produces vicinal diols, which are useful for understanding the stereochemistry and substitution pattern of the original alkene. The formation of a diol from the alkene is a key step in elucidating the positions of the substituents on the carbon–carbon double bond.

Catalytic Hydrogenation of Alkenes

This concept involves the addition of hydrogen (H2) across a carbon–carbon double bond in the presence of a metal catalyst, such as palladium. The addition is typically syn (both hydrogens add to the same face of the double bond), converting the unsaturated alkene to a saturated alkane. It is used as a diagnostic reaction in structure determination since the consumption of one equivalent of hydrogen indicates the presence of one double bond.

Oxidative Cleavage of Alkenes Using KMnO4 in Acid

When alkenes are oxidatively cleaved by KMnO4 under acidic conditions, the double bond is broken and each of the two sp2 carbons is converted into a carbonyl compound. If a carbon in the double bond has at least one hydrogen, it is typically oxidized further to a carboxylic acid; if it is fully substituted (i.e. lacks any hydrogen), the oxidation stops at the ketone stage. The nature and number of the oxidation fragments provide valuable information regarding the substitution pattern around the double bond in the original molecule.

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