COBALT SCHIFF-BASE COMPLEX-CATALYZED OXIDATION OF PARASUBSTITUTED PHENOLICS - MOLECULAR-ORBITAL CALCULATIONS ON PHENOLIC SUBSTRATES

Results from experimental oxidation reactions of lignin model compound s using Co(salen) have indicated widely differing behavior as a functi on of substitution. Syringyl compounds are uniformly more susceptible to oxidation than the analogous guaiacyl and p-hydroxyl compounds. The current work reports on the completion of molecular orbital calculati ons for the lignin model substrates, in an attempt to rationalize the observed differences in reactivity. The energies of the highest occupi ed molecular orbital (HOMO), charge on the phenolic oxygen, and fronti er molecular orbital coefficients on the phenolic hydrogen are consist ently greater for the syringyl compounds, In addition, syringyl compou nds have lower bond dissociation energies for hydrogen abstraction.