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Issue 20, 2007
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An ab initio and DFT study of some halogen atom transfer reactions from alkyl groups to acyl radical

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Abstract

Ab initio calculations using the 6-311G**, cc-pVDZ, and (valence) double-ζ pseudopotential (DZP) basis sets, with (MP2, QCISD, CCSD(T)) and without (HF) the inclusion of electron correlation, and density functional (BHandHLYP, B3LYP) calculations predict that the transition states for the reaction of acetyl radical with several alkyl halides adopt an almost collinear arrangement of attacking and leaving radicals at the halogen atom. Energy barriers (ΔE) for these halogen transfer reactions of between 89.2 (chlorine transfer from methyl group) and 25.3 kJ mol–1 (iodine transfer from tert-butyl group) are calculated at the BHandHLYP/DZP level of theory. While the difference in forward and reverse energy barriers for iodine transfer to acetyl radical is predicted to be 15.1 kJ mol–1 for primary alkyl iodide, these values are calculated to be 6.7 and –4.2 kJ mol–1 for secondary and tertiary alkyl iodide respectively. These data are in good agreement with available experimental data in that atom transfer radical carbonylation reactions are sluggish with primary alkyl iodides, but proceed smoothly with secondary and tertiary alkyl iodides. These calculations also predict that bromine transfer reactions involving acyl radical are also feasible at moderately high temperature.

Graphical abstract: An ab initio and DFT study of some halogen atom transfer reactions from alkyl groups to acyl radical

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Publication details

The article was received on 09 Jul 2007, accepted on 20 Aug 2007 and first published on 05 Sep 2007


Article type: Paper
DOI: 10.1039/B710449A
Org. Biomol. Chem., 2007,5, 3320-3324

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    An ab initio and DFT study of some halogen atom transfer reactions from alkyl groups to acyl radical

    H. Matsubara, I. Ryu and C. H. Schiesser, Org. Biomol. Chem., 2007, 5, 3320
    DOI: 10.1039/B710449A

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