Predictive Kinetic Modeling of Low-Temperature Hydrocarbon Oxidation

Low temperature oxidation in the gas and condensed phases has been the subject of experimental investigations for many decades owing to applications in many areas of practical significance like thermal stability, combustion, atmospheric chemistry and industrial syntheses. Owing to several practical limitations it has proven difficult to understand these processes at a mechanistic level from experiments alone. Developments in scientific computing have opened up computational chemistry and cheminformatics based tools as an attractive option for exploring and elucidating the kinetics of these complex processes through detailed kinetic modeling and requires efforts in three key areas: single reaction kinetics, reaction networks and coupling kinetics with mass/momentum/energy balance models. This thesis presents several contributions employing high-level electronic structure calculations, reaction rate theory, automated kinetic modeling and empirical correlations to further our mechanistic understanding of low-temperature oxidation in the gas and liquid phase. First, an extensible framework for automatic estimation of species thermochemistry in the solution phase is presented and validated. This framework uses the Linear Solvation Energy Relationship (LSER) formalism of Abraham/Mintz and co-workers for high-throughput estimation of ∆G◦ solv(T) in over 30 solvents using solute descriptors estimated from group additivity. The performance of scaled particle theory (SPT) expressions for enthalpic-entropic decomposition of ∆G◦ solv(T) is also discussed along with the associated computational issues. Second, the importance of solvent effects on free-radical kinetics is explored using tetralin oxidation as a case study. The solvent dependence for the main propagation and termination reactions are determined using the Polarizable Continuum (PCM) family of solvation models. Incorporating these kinetic solvent effects in detailed kinetic models suggest oxidation rates increase with solvent polarity, consistent with experiment. Following this, electronic structure methods and reaction rate theory are used elucidate mechanistic details of new pathways in liquid-phase and atmospheric oxidation. The first of these studies focuses on pathways that establish γ-ketohydroperoxides (KHP), well-known products in low-temperature alkane oxidation, as precursors to acids through a two-step process. Ab initio calculations are used to