Question

(a) Limonene, when treated with excess \[{H_2}\] ​ & \[Pt\] catalyst, the product formed, is 1-isopropyl-4-methylcyclohexane 
(b) When it is treated with \[{O_3}\] & then \[Zn/{H_2}O\;\] the products of the reaction are HCHO & above compound
What is the structure of limonene?

Answer 1

Hint:${H_2}$ and Pt catalysts are used in the hydrogenation reaction. In hydrogenation reaction unsaturated compound is converted into saturated compound.
In ozonolysis reaction, unsaturated bonds of alkene, alkyne are cleaved with ozone and multiple carbon-carbon bonds have been replaced by carbonyl groups.

Complete step by step answer:
Structure of limonene is

a.When limonene is treated with hydrogen in presence of platinum catalyst hydrogenation reaction occurs. In hydrogenation reaction carbon-carbon double or triple bond is converted into carbon-carbon single bond. That unsaturated compound is converted into saturated compound so, when limonene undergoes hydrogenation reaction it gives 1-isopropyl-4-methylcyclohexane.
The reaction is:

b.In ozonolysis reaction , unsaturated bonds of alkene, alkyne are cleaved with ozone and multiple carbon-carbon bonds has been replaced by carbonyl group.so when limonene is treated with ozone in presence of \[Zn/{H_2}O\] , The ozone is added across carbon-carbon double bond and it converted into carbonyl group and it gives above compound and formaldehyde(HCHO).
The reaction is:

Zinc dust is used in ozonolysis to prevent the further oxidation of compounds. Zn prevents the compound from further making bonds with oxygen and thus stops the process there.

Additional information: Limonene is a colourless liquid aliphatic hydrocarbon classified as a cyclic monoterpene. And is the major component in the oil of citrus fruit.
Limonene has several applications like used in weight loss, prevent cancer, and treat cancer, treating bronchitis. Used as a flavouring, chewing gum, beverages.

Note:
The molecular formula of limonene is ${C_{10}}{H_{16}}$. Inhalation of limonene vapour increases serotonin and dopamine levels and causes anxiety, depression.
Limonene is a chiral molecule hence obtained as D-limonene and L-limonene.