(or 1,3-pentadiene),

¹CH₂—²CH—³CH—⁴CH—⁵CH₃

a colorless liquid, insoluble in water but soluble in most organic solvents. Piperylene exists in the cis- and trans- forms (boiling points, 44.07°C and 42.03°C; densities at 20°C, 0.691 and 0.676 g/cm³, respectively). It enters into all reactions characteristic of conjugated diene hydrocarbons.

Piperylene is found in petroleum cracking products; it is a by-product of isoprene synthesis (from isobutylene and formaldehyde) and can also be obtained by dehydrogenation of n-pentenes. It polymerizes and copolymerizes readily—for example, with isoprene and styrene.