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Title: Computational Study of Bond Dissociation Enthalpies for Substituted $$\beta$$-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 $$\beta$$-O-4 ether linkage. Density functional theory (DFT) is used to calculate the Boltzmann-weighted carbon-oxygen and carbon-carbon bond dissociation enthalpies (BDEs) of substituted PPE. These values are important in order to understand 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, where 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:
 [1];  [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Center for Computational Sciences
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1033523
DOE Contract Number:  
DE-AC05-00OR22725
Resource Type:
Journal Article
Journal Name:
ChemPhysChem
Additional Journal Information:
Journal Volume: 12; Journal Issue: 18; Journal ID: ISSN 1439-4235
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; 09 BIOMASS FUELS; BENCHMARKS; BONDING; DISSOCIATION; ETHERS; FUNCTIONALS; HYDROGEN; LIGNIN; OXYGEN; PHENYL ETHER; THERMODYNAMICS; lignin; bond dissociation enthalpy; BDE; density functional theory; DFT; hydrogen bonding; phenethyl phenyl ether; PPE

Citation Formats

Younker, Jarod M, Beste, Ariana, and Buchanan, III, A C. Computational Study of Bond Dissociation Enthalpies for Substituted $\beta$-O-4 Lignin Model Compounds. United States: N. p., 2011. Web. doi:10.1002/cphc.201100477.
Younker, Jarod M, Beste, Ariana, & Buchanan, III, A C. Computational Study of Bond Dissociation Enthalpies for Substituted $\beta$-O-4 Lignin Model Compounds. United States. doi:10.1002/cphc.201100477.
Younker, Jarod M, Beste, Ariana, and Buchanan, III, A C. Sat . "Computational Study of Bond Dissociation Enthalpies for Substituted $\beta$-O-4 Lignin Model Compounds". United States. doi:10.1002/cphc.201100477.
@article{osti_1033523,
title = {Computational Study of Bond Dissociation Enthalpies for Substituted $\beta$-O-4 Lignin Model Compounds},
author = {Younker, Jarod M and Beste, Ariana and Buchanan, III, A C},
abstractNote = {The biopolymer lignin is a potential source of valuable chemicals. Phenethyl phenyl ether (PPE) is representative of the dominant $\beta$-O-4 ether linkage. Density functional theory (DFT) is used to calculate the Boltzmann-weighted carbon-oxygen and carbon-carbon bond dissociation enthalpies (BDEs) of substituted PPE. These values are important in order to understand 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, where 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.},
doi = {10.1002/cphc.201100477},
journal = {ChemPhysChem},
issn = {1439-4235},
number = 18,
volume = 12,
place = {United States},
year = {2011},
month = {1}
}