Unimolecular Photodissociation of s-Tetrazine and Derivatives

Article abstract of DOI:10.1021/j100330a010

Quantum yields measured for the photofragmentation reaction of vapor-phase s-tetrazines indicate the chromophore undergoes unimolecular dissociation via a vibrationally hot ground-state molecule.Collisional quenching is used to determine reaction rates for s-terazine, 3,6-dimethyl-s-tetrazine, and 3-phenyl-s-tetrazine.A comparison of the reaction rate constants shows that vibrational energy redistribution from the tetrazine ring to methyl or phenyl substituents occurs in less than 1 ns.The activation energy for dissociation is measured to be 39.7 and 40.1 kcal mol^-1 for gaseous s-tetrazine and 3,6-dimethyl-s-tetrazine, respecticely.RRKM theory is applied using the measured thermal parameters.The microcanonical rate constants predicted by RRKM theory underestimate the experimentally measured values.The disagreement may be accounted for by a more detailed description of the force field for the critical configuration.