Application of the Group Additivity Method to Alkyl Radicals: An ab Initio Study

István Marsi, B. Viskolcz, László Seres

Research output: Article

34 Citations (Scopus)

Abstract

The geometries and standard enthalpies of formation (Δf(H°) of 4 paraffins and 31 alkyl radicals at 298 K were obtained by means of complete basis set 4 (CBS-4) ab initio molecular orbital theory. A comparison of the geometry of a molecule and the radicals derivable from it via elimination of a H atom from different positions suggests that only a negligible change occurs in the geometry of the groups immediately adjacent to the radical center. The CBS-4 ΔfH°s scaled by an empirical correction display an average deviation of 0.4 kcal mol-1 from the experimental data. Group values (GVs) were evaluated from the corrected ab initio ΔfH°s by simultaneous parameter estimation. The group additivity (GA) rule was checked by a statistical analysis of the theoretical data. The derived GVs describe the corrected ab initio ΔfH°s with an average deviation of less than 0.3 kcal mol-1, which indicates that the GA rule is applicable to alkyl radicals, and the Δ/fH°s of alkyl radicals can be predicted with an accuracy similar to that attained with existing experimental methods. New values of radical, radical-adjacent, and (C)2-C-C-(C) gauche GVs are suggested; together with the accepted alkane GVs, these yield accurate ΔfH°s of alkyl radicals within estimated errors of 0.5 kcal mol-1. Application of the GVs derived from small species is predicted to perform less satisfactorily in the estimation of ΔfH°s of C4-C6 species: the average deviation increases from 0.3 to 0.6 kcal mol-1, while the correlation of the individual deviations and carbon numbers of the alkyl radicals changes from nearly zero to -0.36.

Original languageEnglish
Pages (from-to)4497-4504
Number of pages8
JournalJournal of Physical Chemistry A
Volume104
Issue number19
Publication statusPublished - 2000

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Geometry
Alkanes
Molecular orbitals
deviation
Paraffin
Parameter estimation
Enthalpy
Statistical methods
Carbon
Atoms
Molecules
geometry
paraffins
statistical analysis
alkanes
elimination
molecular orbitals
enthalpy
carbon
atoms

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Application of the Group Additivity Method to Alkyl Radicals : An ab Initio Study. / Marsi, István; Viskolcz, B.; Seres, László.

In: Journal of Physical Chemistry A, Vol. 104, No. 19, 2000, p. 4497-4504.

Research output: Article

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