C5H8

C5H8 describes a molecular formula that corresponds to several different hydrocarbons containing five carbon atoms and eight hydrogen atoms. Because the formula has two degrees of unsaturation, the isomers include cycloalkenes and open-chain dienes. The most prominent representatives are isoprene (2-methyl-1,3-butadiene) and simple pentadienes such as 1,3-pentadiene and 1,4-pentadiene, as well as cyclopentene.

Isoprene is the best known C5H8 isomer. It is a volatile liquid at room temperature and is the primary biogenic and industrial building block for natural rubber and related polymers. Other C5H8 isomers occur in smaller amounts or are of academic interest, and they find use in specialized chemical syntheses or serve as intermediates in fragrance chemistry.

Because multiple structures share the same molecular formula, C5H8 by itself provides no information about connectivity or stereochemistry. Properties such as boiling point, density, and reactivity depend strongly on the specific isomer. All C5H8 compounds are hydrocarbons and are typically flammable and must be handled with appropriate safety precautions.