title: Computational study of bond dissociation enthalpies for substituted β-O-4 lignin model compounds.
abstract: The biopolymer lignin is a potential source of valuable chemicals. Phenethyl phenyl ether (PPE) is representative of the dominant β-O-4 ether linkage. DFT is used to calculate the Boltzmann-weighted carbon-oxygen and carbon-carbon bond dissociation enthalpies (BDEs) of substituted PPE. These values are important for understanding lignin decomposition. Exclusion of all conformers that have distributions of less than 5% at 298 K impacts the BDE by less than 1 kcal mol(-1). We find that aliphatic hydroxyl/methylhydroxyl substituents introduce only small changes to the BDEs (0-3 kcal mol(-1)). Substitution on the phenyl ring at the ortho position substantially lowers the C-O BDE, except in combination with the hydroxyl/methylhydroxyl substituents, for which the effect of methoxy substitution is reduced by hydrogen bonding. Hydrogen bonding between the aliphatic substituents and the ether oxygen in the PPE derivatives has a significant influence on the BDE. CCSD(T)-calculated BDEs and hydrogen-bond strengths of ortho-substituted anisoles, when compared with M06-2X values, confirm that the latter method is sufficient to describe the molecules studied and provide an important benchmark for lignin model compounds.
authors: Oak Ridge Associated Universities, 1 Bethel Valley Road, Oak Ridge, Tennessee, 37831-6164, USA. younkerjm@ornl.gov
authors: Jarod M
authors: JM
authors: Younker
authors: Ariana
authors: A
authors: Beste
authors: A C
authors: AC
authors: Buchanan
mesh_terms: D006860:Hydrogen Bonding; D008031:Lignin / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D010647:Phenyl Ethers / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D010647:Phenyl Ethers; D008031:Lignin