Figure 123.
Terpenes may be cyclic or linear with more than 23,000 terpenes known in nature. The simple terpenes like myrcene have a molecular formula of C10H15 with multiples of five carbons added to make C15, C20, C25, etcetera, as numbers of carbon atoms per terpene. Terpenes do not have to have double bonds and can be substituted with ketones and hydroxyl groups. Menthol, limonene, and camphor are examples of terpenes. Certain molecules in plants, such as vitamin A and beta-carotene, are considered terpenes. Figure 124 shows terpenes that are fragrant in nature:
Figure 124.
STEROIDS Steroids are lipids by virtue of being lipid soluble and hydrophobic. These are essentially specific types of terpenes that have a common polycyclic framework. Figure 125 shows what a numbered steroid ring looks like with the rings labelled A, B, C, and D:
226