Question

One of the principal components of lemongrass oil is limonene, . When limonene is treated with excess hydrogen and a platinum catalyst, the product is an alkane of formula . What can you conclude about the structure of limonene?

Short answer

Limonene must have one ring and two double bonds or a triple bond.

Step-by-step solution

Limonene

Limonene has three degrees of unsaturation. Hydrogenation reaction has proved this, as upon catalytic hydrogenation, that is, treatment of limonene with excess hydrogen and platinum as a catalyst, the product gets formed which has only one degree of unsaturation.

Structure of Limonene

Two degrees of unsaturation have been removed by hydrogenation reaction, and these must be two double bonds or one triple bond. The remaining unsaturation must be a ring. Thus, limonene must have one ring and either two double bonds or one triple bond.