Q8-58 E-a - Organic Chemistry (Mcmurry)

Question

Compound A has the formula ${\mathbf{C}}_{\mathbf{10}}{\mathbf{H}}_{\mathbf{16}}$. On catalytic hydrogenation over palladium, it reacts with only 1 molar equivalent of ${\mathbf{H}}_{\mathbf{2}}$. Compound A also undergoes reaction with ozone, followed by zinc treatment, to yield a symmetrical diketone, $\mathbf{B}\left(C_{10}{H}_{16}{O}_2\right)$.

How many rings does A have?

Step-by-Step Solution

Answer

Answer

 

Two rings

Step 1: Catalytic hydrogenation

Catalytic hydrogenation is the reaction of alkene or alkyne with hydrogen in the presence of a metal catalyst like nickel, palladium, or platinum. Hydrogenation reduces double and triple bonds in hydrocarbons and adds hydrogen.

Step 2: O 3 and Zn reactions

When an alkene is treated with ozone and subjected to reductive workup with zinc, the carbon-carbon double bond is cleaved to give ketones or aldehydes, which depend on the alkene structure.

Step 3: Reaction interpretation

• In the reaction, as only 1 mole of dihydrogen is used, it indicates only one bond is broken, and only two hydrogens are attached to 1 mole ${\mathrm{C}}_{10}{\mathrm{H}}_{16}$. 
• As here, O₃  and Zn are used in the second step, which results in symmetrical diketone formation, this indicates the presence of one ene group
• Symmetrical diketone presence indicates that carbons having double bonds have no hydrogen; otherwise, aldehyde will form.
• So, there must be two rings in compound A having a double bond between them.

Step 4: Rings in compound A

Two rings in compound A