Computational Study of Bond Dissociation Enthalpies for Lignin Model Compounds: $beta$-5 Arylcoumaran

Abstract

The biopolymer lignin is a potential source of valuable chemicals. The $beta$-5 linkage comprises $sim$10% of the linkages in lignin. Density Functional Theory (DFT) was used to calculate the $alpha$C-O and $alpha$C-$beta$C bond dissociation enthalpies (BDEs) for $beta$-5 models with varied substituents, which are important for understanding initial lignin decomposition. The $alpha$C-O ($alpha$C-$beta$C) 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.