Multiorbital interactions during acyl radical addition reactions involving imines and electron-rich olefins

Kyne, S. H., Schiesser, C. H. and Matsubara, H. (2008) Multiorbital interactions during acyl radical addition reactions involving imines and electron-rich olefins. Journal of Organic Chemistry, 73 (2). pp. 427-434. ISSN 0022-3263

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Ab initio and DFT calculations reveal that acyl radicals add to imines and electron-rich olefins through simultaneous SOMO-pi*,pi- SOMO, and HOMO-pi*C=O interactions between the radical and the radicalophile. At the CCSD(T)/aug-cc-pVDZ//QCISD/cc- pVDZ level, energy barriers of 15.6 and 17.9 kJ mol-1 are calculated for the attack of the acetyl radical at the carbon and nitrogen ends of methanimine, respectively. These barriers are 17.1 and 20.4 kJ mol-1 at BHandHLYP/cc-pVDZ. In comparison, barriers of 34.0 and 23.4 kJ mol -1 are calculated at BHandHLYP/cc-pVDZ for reaction of the acetyl radical at the 1- and 2-positions in aminoethylene, repectively. Natural bond orbital (NBO) analysis at the BHandHLYP/6-311G** level of theory reveals that SOMO-pi*imine, piimine-SOMO, and LPN-pi*C=O interactions are worth 90, 278, and 138 kJ mol-1, respectively, in the transition state (2) for reaction of acetyl radical at the nitrogen end of methanimine; similar interactions are observed for the chemistry involving aminoethylene. These multiorbital interactions are responsible for the unusual motion vectors associated with the transition states involved in these reactions. NBO analyses for the remaining systems in this study support the hypothesis that the acetyl radical is ambiphilic in nature.

Keywords:Ab initio structural calculations, Density functional theory, Intermolecular radical addition, Imine
Subjects:F Physical Sciences > F160 Organic Chemistry
F Physical Sciences > F190 Chemistry not elsewhere classified
Divisions:College of Science > School of Chemistry
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ID Code:17621
Deposited On:12 Jun 2015 04:30

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