Question

If the following sesquiterpene is synthesized in a medium containing acetate with a ¹⁴C-labeled carbonyl carbon, which carbons will be labeled?

Short answer

Carotenoids are tetraterpenes (40 carbons). Lycopene, the compound responsible for the red coloring of tomatoes and watermelon, and b-carotene, the compound that causes carrots and apricots to be orange, are carotenoids.

Step-by-step solution

Carotenoids

Carotenoids are tetraterpenes (40 carbons). Lycopene, the compound responsible for the red coloring of tomatoes and watermelon, and b-carotene, the compound that causes carrots and apricots to be orange, are carotenoids.

Identification of labelled carbon

The given sesquiterpene is produced from farnesyl pyrophosphate via cyclization followed by loss of a proton from the carbocation. Since, in farnesyl pyrophosphate C-2,C-4,C-6,C-8,C-10 and C-12 are labeled ¹⁴C carbons. Hence, labeled carbons in given sesquiterpene is as follows:

Structure of the desired product