Question

A hydrocarbon ' $X$ ' with formula $C _6 H _8$ uses two moles of $H _2$ on catalytic hydrogenation of its one mole On ozonolysis, ' $X$ ' yields two moles of methane dicarbaldehyde The hydrocarbon ' $X$ ' is :

• A. hexa-1, 3, 5-triene
• B. 1-methylcyclopenta-1, 4-diene
• C. cyclohexa - 1, 3-diene
• D. cyclohexa-1, 4-diene

Hint:

Ozonolysis of conjugated dienes typically produces aldehydes or ketones depending on the position of the double bonds.

Answer 1

The Correct Option is D

To solve this problem, we need to determine which hydrocarbon matches the properties described: namely, a hydrocarbon with the formula \(C_6H_8\), that uses two moles of \(H_2\) on catalytic hydrogenation and yields two moles of methane dicarbaldehyde upon ozonolysis.

1. The molecular formula \(C_6H_8\) suggests it could be an unsaturated hydrocarbon with multiple bonds, as it has fewer hydrogens than the saturated alkane would (\(C_6H_{14}\)).
2. During catalytic hydrogenation where two moles of \(H_2\) are used, two double bonds must be present since hydrogenation involves the breaking of these double bonds.
3. Ozonolysis results in the formation of two moles of methane dicarbaldehyde, suggesting the presence of a diene (two double bonds in conjugation) that forms diketones or dialdehydes upon such reaction.
4. Among the given options:
   • hexa-1, 3, 5-triene: This compound has three double bonds, which is inconsistent with the hydrogenation information (it uses three moles of \(H_2\)).
   • 1-methylcyclopenta-1, 4-diene: This compound, being a different ring structure, would not yield two molecules of identical dialdehyde upon ozonolysis.
   • cyclohexa-1, 3-diene: With only two double bonds, it would produce one or more different ozonolysis products due to the internal structure of the ring.
   • cyclohexa-1, 4-diene: This compound has two non-conjugated double bonds at alternative positions (1,4). Ozonolysis of the 1,4-diene would ideally lead to cleaving across these double bonds to form two identical dialdehyde molecules as described.
5. Thus, the behavior described fits best with cyclohexa-1, 4-diene, as it would yield two moles of methane dicarbaldehyde upon ozonolysis and will use two moles of \(H_2\) for hydrogenation, thereby matching all the conditions of the question.

Therefore, the correct answer is cyclohexa-1, 4-diene.