The biopolymer lignin is a potential source of valuable chemicals. The beta-5 linkage comprises similar to 10% of the linkages in lignin. Density Functional Theory (DFT) was used to calculate the C-alpha-O and C-alpha-C-beta bond dissociation enthalpies (BDEs) for beta-5 models with varied substituents, which are important for understanding initial lignin decomposition. The C-alpha-O (C-alpha-C-beta) 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. (C) 2012 Elsevier B.V. All rights reserved.