Some aspects of the solution photochemistry of 1,3‐cyclohexadiene, (Z)‐ and (E)‐1,3,5‐hexatriene

UV irradiation (λ = 265 nm) of 1,3‐cyclohexadiene yields ( Z )‐1,3,5‐hexatriene with good efficiency (Φ = 0.41). UV irradiation also effects equilibration between ( Z )‐ and ( E )‐isomers, be it with rather low quantum yields (Φ Z→E = 0.034; Φ Z→E =0.016). The Z ⇄ E isomerization can be sensitized by triplet sensitizers, e.g. biacetyl. This reaction occurred also upon irradiation of solutions in bromoform with light of 436 nm (S o → T absorption). A simple formula for the calculation of quantum yields from composition data is given.