Contra-thermodynamic behavior in intermolecular hydrogen transfer of alkylperoxy radicals

Jim Pfaendtner, Linda J. Broadbelt*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

Abstract

Quantum chemical investigation of bimolecular hydrogen transfer involving alkylperoxy radicals, a key reaction family in the free-radical oxidation of hydrocarbons, was performed to establish structure-reactivity relationships. Eight different reactions were investigated featuring four different alkane substrates (methane, ethane, propane and isobutane) and two different alkylperoxy radicals (methylperoxy and iso-propylperoxy). Including forward and reverse pairs, sixteen different activation energies and enthalpies of reaction were used to formulate structure-reactivity relationships to describe this chemistry. We observed that the enthalpy of formation of loosely bound intermediate states has a strong inverse correlation with the overall heat of reaction and that this results in unique contra-thermodynamic behavior such that more exothermic reactions have higher activation barriers. A new structure-reactivity relationship was proposed that fits the calculated data extremely well: EA = Eo + αΔHrxn where α = -0.70 for ΔHrxn < 0, and α = 1.10 for ΔHrxn > 0 and Eo = 3.05 kcal mol-1.

Original languageEnglish (US)
Pages (from-to)1969-1978
Number of pages10
JournalChemPhysChem
Volume8
Issue number13
DOIs
StatePublished - Sep 17 2007

Keywords

  • Ab initio calculations
  • Density functional calculations
  • Hydrogen bonds
  • Hydrogen transfer
  • Radicals

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Physical and Theoretical Chemistry

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