Knowledge Bank

Beside the two benzine- like $\pi \pi \ast$ transitions occurring in both of these molecules in this region, several additional transitions have been previously reported including a Rydberg transition in pyrazine, and a possible $n\pi \ast$ or Rydberg transition in pyridazine. To obtain additional information on these transitions, we have studied them in perfluorohexane both in the presence and absence of several hydrogen bonding fluoroalchols. Our solvent perturbation technique shows that some vibionic bands thought to be part of a shingle transition in pyrazine show different solvent shifts and hence probably involve vibrations of at least two different electronic states. The solvent effects on the relatively sharp band system in pyridazine starting around 200 nm will be reported and the possible assignments discussed. In both molecules a new broad transition between 200 and 240 nm is revealed by hydrogen bonding studies which appears to be of $n\pi \ast$ character.