Abstract
Lignin is an abundant natural resource that is a potential source of valuable chemicals. Improved understanding of the pyrolysis of lignin occurs through study of model compounds for which phenethyl phenyl ether (PhCH2CH2OPh, PPE) is the simplest example representing the dominant �-O-4 ether linkage. The pyrolysis of PPE proceeds through a free radical chain mechanism involving two competitive pathways (�/�-selectivity) abstracting hydrogen whether on the �- or �-site of PPE. Naturally occurring substituents (hydroxy, methoxy) have a large influence on reaction rates and product distribution. In this work, we investigate the effect of methoxy substituents located at the phenoxy ring on hydrogen abstraction reactions relevant to the pyrolysis of substituted PPE. We use density functional methods to calculate reaction energies and barriers for �- and �-pathways of the appropriate reactions. We find that the substituent effect is particularly large for the reaction energies of the hydrogen abstraction reactions by the phenoxy radicals. Also, the �/�-barrier difference is significantly influenced by the substituents and will largely affect the experimentally observed �/�-selectivity.