hexatrien

Hexatriene is a hydrocarbon consisting of six carbon atoms and three conjugated carbon–carbon double bonds. The term most commonly refers to 1,3,5-hexatriene, with the linear structure CH2=CH-CH=CH-CH=CH2 and the formula C6H8. The three double bonds are alternated by single bonds, giving an extended pi system.

The conjugated pi system of hexatriene gives it distinct electronic properties and reactivity. It is typically highly reactive and is often encountered only as a transient intermediate or within stabilized derivatives in laboratory settings. In solution, its reactivity is governed by the extended conjugation, which also influences its ultraviolet absorption characteristics.

Geometric isomerism can arise on the interior double bonds, leading to several conformers, while the terminal double bond (the CH2= end) cannot exhibit E/Z isomerism because the terminal carbon bears two identical substituents (two hydrogens).

Hexatriene serves as a classic model compound in the study of pericyclic reactions. It undergoes electrocyclic ring closure to cyclohexadiene through a 6π electron system. According to the Woodward–Hoffmann rules, this thermal electrocyclization proceeds conrotatorily, whereas the photochemical version would be disrotatory. This makes hexatriene a standard example for exploring orbital symmetry in organic chemistry.

Synthesis and occurrence are typically in situ or within stabilized derivatives, as the pure molecule is highly reactive and not commonly isolated under normal laboratory conditions.