Computational study of bond dissociation enthalpies for lignin model compounds: β-5 Arylcoumaran

The biopolymer lignin is a potential source of valuable chemicals. The β-5 linkage comprises ∼10% of the linkages in lignin. Density Functional Theory (DFT) was used to calculate the Cα–O and C α – C β bond dissociation enthalpies (BDEs) for β-5 models with varied substituents, which are important for understanding initial lignin decomposition. The Cα–O ( C α – C β ) BDEs were in the range of 40–44 (57–62) kcal/mol. The products resulting from either homolysis are bi-radicals with multi-determinant character in the singlet electronic state. Multiconfiguration self-consistent field (MCSCF) theory results were used to verify that unrestricted DFT and broken-symmetry DFT were sufficient to study these reactions.