Exploration of Hydrogen atom transfers in alkyl, alkenyl, and functionalized radicals, as predicted by composite ab initio methods

Carrigan J. Hayes and Donald R. Burgess, Jr.

Kinetic modeling of fuels relies heavily on automatic mechanism generation, an approach which utilizes Evans-Polyani relationships to quickly calculate kinetic parameters from thermodynamic data, efficiently producing a variety of kinetic information for the large number of elementary reaction steps involved in combustion of a given fuel.  Both mechanism generation and kinetic modeling approaches are likely to play increasingly important roles in predicting alternative fuel chemistry, as society shifts away from dependence on primarily-hydrocarbon-derived fuels.  Thus, it is imperative that these generated kinetic parameters be accurate.  Isomerizations (internal hydrogen-atom transfers) dictate a substantial portion of low-temperature combustion.  These reactions and this temperature range greatly impact alternative fuels and engine performance.  High-level composite ab initio methods (G3MP2B3) were used to explore the H-atom transfers possible for a variety of reactive species, including alkyl, alkenyl, cycloalkyl, and oxoallylic (derived from aldehydes and ketones) radicals.  For alkyl radicals, a pronounced correlation between enthalpies of activation and enthalpies of reaction was seen (such that an Evans-Polyani relationship could be derived); however, this scaling behavior was not seen in the functionalized radicals.  The non-Evans-Polyani behavior of these functionalized radicals is significant and has implications for alternative fuel mechanism generation.        

Carrigan J. Hayes

Mentor: Dr. Donald Burgess, Jr.

National Institute of Standards and Technology

Division of Chemical and Biochemical Reference Data

Chemical Science and Technology Laboratory

Building 221, Room B332

100 Bureau Drive, Mail Stop 8320

Gaithersburg, MD 20899-8320

Telephone: 301-975-5478

Fax: 301-869-4020

Email: carrigan.hayes@nist.gov

Poster Category: CHEMISTRY

Sigma Xi Affiliation: none