Trienes

Trienes are organic compounds that contain three carbon–carbon double bonds in their carbon framework. The arrangement of these double bonds determines key properties and reactivity, and trienes can be categorized as conjugated, cumulated, or isolated.

In conjugated trienes, the double bonds alternate with single bonds (for example CH2=CH-CH=CH-CH=CH2, 1,3,5-hexatriene). Conjugation extends the pi-system, lowering the energy of electronic transitions and often producing significant UV–visible absorption and colored compounds. Conjugated trienes are common in natural pigments and in synthetic dyes and in precursors to aromatic rings.

Cumulated trienes feature consecutive double bonds that share a common carbon, a arrangement seen in allenes and related species (for instance CH2=C=C=CH2, a butatriene). These are typically less stable and have different reactivity profiles compared with conjugated trienes, including distinct stereochemistry and pericyclic behavior.

Isolated trienes have their three double bonds separated by at least one single bond, reducing interaction between pi-systems and generally diminishing conjugation effects.

Trienes occur in natural products as parts of larger polyenes, such as carotenoids, and serve as versatile intermediates in organic synthesis. They participate in photochemical isomerization and various cycloaddition and rearrangement reactions; the conjugated subset is especially important in materials chemistry and dye chemistry.

Overall, trienes illustrate how the arrangement of multiple double bonds influences stability, light absorption, and chemical reactivity in unsaturated systems.