Competition between alkyl radical addition to carbonyl bonds and H-atom abstraction reactions

Horst Hippler, B. Viskolcz

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

The activation energies for the methyl radical addition to CH2O, CH3CHO, and (CH3)2CO, are small and around 28, 29, and 40 kJ mol-1, respectively. For the addition of primary alkyl radicals to formaldehyde and higher aldehyde homologues, we find significantly lower activation barriers of (20 ± 4) kJ mol-1 and (27 ± 2) kJ mol-1, respectively. An almost negligible activation barrier of about 5 kJ mol-1 was found for the secondary radical addition to formaldehyde. In the case of addition of a tertiary radical to formaldehyde no activation barrier could be identified. Generally, methyl addition reactions to carbonyls will compete with hydrogen abstraction reactions. For larger alkyl radicals addition to carbonyls dominates over the direct H-atom abstraction. A self-consistent set of standard enthalpies of formation ΔfH° for saturated alkoxy (CnH2n+1O., where n ≤ 5) radicals was obtained by the modified Gaussian-3 (G3(MP2)//B3LYP) ab initio molecular orbital theory. The calculated heats of formations are in good agreement with literature values estimated from O-H bond dissociation energies. The expected maximum error of the calculated ΔfH° is less than 4 kJ mol-1. The primary, secondary, and tertiary alkoxy group values (GV) were evaluated from the ab initio ΔfH°-s with a standard deviation of 1.2 kJ mol-1.

Original languageEnglish
Pages (from-to)4663-4668
Number of pages6
JournalPhysical Chemistry Chemical Physics
Volume4
Issue number19
DOIs
Publication statusPublished - 2002

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Formaldehyde
Chemical activation
Atoms
formaldehyde
atoms
Addition reactions
activation
Molecular orbitals
Aldehydes
Hydrogen
Enthalpy
Activation energy
heat of formation
aldehydes
standard deviation
molecular orbitals
enthalpy
dissociation
activation energy
alkoxyl radical

ASJC Scopus subject areas

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

Cite this

Competition between alkyl radical addition to carbonyl bonds and H-atom abstraction reactions. / Hippler, Horst; Viskolcz, B.

In: Physical Chemistry Chemical Physics, Vol. 4, No. 19, 2002, p. 4663-4668.

Research output: Contribution to journalArticle

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