Mechanism of the formation of weak complexes of the spatially hindered quinones and phenols

Abstract

1. Study of absorption spectra and molecular models has shown that 3,6-di-tert-butyl-o-benzoquinone and 3,6-di-tert-butylpyrocatechol can form either charge transfer complexes or complexes with two hydrogen bonds (HBC). 2. The ESR spectra suggest the presence of four types of radical pairs in irradiated frozen solutions of quinone and pyrocatechol. A mechanism, involving H-atom phototransfer from the pyrocatechol to the quinone in the binary complex, has been proposed to account for the formation of all radical pairs, and the geometry of the complex established. 3. Differences in the fine structure constants for the deuterated and nondeuterated compounds have been explained in terms of the equilibrium established between the hydrogen bonded complexes and the sandwich complexes. The geometry of the sandwich complex varies, depending on whether the complex has been formed from the HBC or from the individual quinone and pyrocatechol molecules.