* Refreshments will be served at 3:30 PM in the Lower Level 1 Gossage Atrium
* Lecture commences at 4:00 PM in L1255 in the Ford ES&T Building

Seminar Abstract
Computer models of complex reacting systems provide important details about reaction paths and reactive intermediates that are often difficult to measure experimentally. Constructing such models requires establishing a reaction mechanism that may contain hundreds of species and thousands of chemical reactions. In recent years mechanistic modeling has successfully been used to study complex reaction mechanisms in systems such as lubricant degradation, polymerization, and atmospheric chemistry.

A general approach for modeling chemical reacting systems will be presented, with specific applications to free-radical oxidation of hydrocarbons and the thermal degradation of lubricating oils. The large numbers of reactive intermediates, stable molecular products and reaction
pathways present in the system makes modeling free-radical oxidation challenging. However,
we have developed a computational framework based on a graph-theory representation of
chemical species and reactions that can generate reaction networks automatically. Such
elementary step reaction networks give detailed information about the product distributions and
controlling reaction pathways. Successful application of this approach requires the accurate
specification of reaction rate coefficients and thermodynamic properties for each reaction.

Quick and reliable estimation of reaction kinetics is essential since complete experimental
characterization of complex reacting systems is not currently possible. Used effectively,
quantum mechanics (QM) can augment our knowledge of chemical reactivity where experiments
have failed to provide sufficient information. In particular, QM has great potential to reveal
structure-reactivity relationships in which some property that is easy to estimate (e.g., the
enthalpy of reaction) is correlated to a measure of chemical reactivity that is difficult to
determine experimentally or calculate from theory (e.g., the activation energy). Structurereactivity
relationships derived from empirical data have been used to study problems in
catalysis, polymers, and biochemistry, but there are comparably few examples where QM has
been used to derive such relationships. Theoretical development of structure-reactivity
relationships for hydrogen transfer reactions of 1) alkyl, alkoxy, and alkylperoxy radicals and 2)
hindered-phenol antioxidants will be discussed.