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Ab initio group contribution method for activation energies for radical additions
Author(s) -
Saeys Mark,
Reyniers MarieFrançoise,
Marin Guy B.,
Van Speybroeck Veronique,
Waroquier Michel
Publication year - 2004
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.10038
Subject(s) - chemistry , ab initio , radical , additive function , computational chemistry , activation energy , ab initio quantum chemistry methods , standard enthalpy of formation , bond cleavage , thermodynamics , organic chemistry , molecule , catalysis , physics , mathematical analysis , mathematics
Accurate activation energies for 67 hydrocarbon radical addition and β‐scission reactions are calculated with the CBS‐QB3 ab initio method. An extension of Benson's group additivity method to activation energies is introduced. The underlying hypotheses, that is, the group concept and the additivity approximation, are validated with ab initio data. Standard activation group additivity values are obtained from the ab initio calculations for reactions involving primary, secondary, tertiary alkylic, allylic, benzylic, and vinylic radicals. The proposed group contribution method yields accurate activation energies for radical addition and for β‐scission reactions. The effect of substituents on the carbon atoms of the reactive center on the activation energy can be as large as 95 kJ/mol for the adding radical, and 187 kJ/mol for the product radical of the β‐scission. Non‐nearest‐neighbor effects such as gauche and cis interactions have an influence of less than 3 kJ/mol per interaction on the activation energies. However, for hydrocarbons that are heavily branched near the reactive center, these interactions can become important. © 2004 American Institute of Chemical Engineers AIChE J , 50: 426–444, 2004