Ab initio studies of carbonyl radical additions to hydrazone systems

Ab initio and DFT calculations reveal that intermolecular radical additions of both acyl and oxyacyl radials to hydrazones occur through SOMO-pi*hydrazone, pihydrazone-SOMO and LPN-SOMO interactions between the radical and the hydrazone pi-system. Both acetyl and methoxycarbonyl radicals show preference for addition to the carbon end of the carbon-nitrogen pi-bond. At the highest level of theory used in this study (G2//MP2(full)/6-31G*), energy barriers of 11.2 and 22.6 kJ mol1 are calculated for acetyl radical addition to the carbon and nitrogen-ends of N-aminomethanimine respectively. The analogous energy barriers for the methoxycarbonyl radical are 4.9 and 25.7 kJ mol -1 at the same level of theory.</p

Ab initio studies of carbonyl radical additions to hydrazone systems

Ab initio and DFT calculations reveal that intermolecular radical additions of both acyl and oxyacyl radials to hydrazones occur through SOMO-pi*hydrazone, pihydrazone-SOMO and LPN-SOMO interactions between the radical and the hydrazone pi-system. Both acetyl and methoxycarbonyl radicals show preference for addition to the carbon end of the carbon-nitrogen pi-bond. At the highest level of theory used in this study (G2//MP2(full)/6-31G*), energy barriers of 11.2 and 22.6 kJ mol1 are calculated for acetyl radical addition to the carbon and nitrogen-ends of N-aminomethanimine respectively. The analogous energy barriers for the methoxycarbonyl radical are 4.9 and 25.7 kJ mol -1 at the same level of theory.</p

An ab initio and DFT study of radical addition reactions of imidoyl and thioyl radicals to methanimine

Ab initio and DFT calculations reveal that both imidoyl and thioyl radicals add to the nitrogen end of methanimine through simultaneous SOMO-pi*imine, SOMO-piimine, SOMO-LPN and pi*radical-LPN interactions between the radical and the imine. At the CCSD(T)/cc-pVDZ//BHandHLYP/cc-pVTZ level of theory, barriers of 13.8 and 26.1 kJ mol-1 are calculated for the attack of the methylimidoyl radical at the carbon- and nitrogen- end of methanimine, respectively, indicating that the imidoyl radial has a preference for addition to the nitrogen end of imine. On the other hand, barriers of 25.1 and 13.4 kJ mol-1 are calculated at the same level of theory for the addition reaction of the methanethioyl radical at the carbon- and nitrogen- end of methanimine, respectively. Natural bond orbital (NBO) analysis at the BHandHLYP/6-311G** level of theory reveals that SOMO-pi*imine, SOMO-piimine, SOMO-LPN and pi*radical-LPN interactions are worth 111, 89, 115 and 17 kJ mol-1, respectively, in the transition state (4) for the reaction of methylimidoyl radical at the nitrogen end of methanimine; similar interactions are observed for the chemistry involving all the radicals studied here. These multi-component interactions are responsible for the unusual motion vectors associated with the transition states involved in these reactions.</p

An ab initio and DFT study of radical addition reactions of imidoyl and thioyl radicals to methanimine

Ab initio and DFT calculations reveal that both imidoyl and thioyl radicals add to the nitrogen end of methanimine through simultaneous SOMO-pi*imine, SOMO-piimine, SOMO-LPN and pi*radical-LPN interactions between the radical and the imine. At the CCSD(T)/cc-pVDZ//BHandHLYP/cc-pVTZ level of theory, barriers of 13.8 and 26.1 kJ mol-1 are calculated for the attack of the methylimidoyl radical at the carbon- and nitrogen- end of methanimine, respectively, indicating that the imidoyl radial has a preference for addition to the nitrogen end of imine. On the other hand, barriers of 25.1 and 13.4 kJ mol-1 are calculated at the same level of theory for the addition reaction of the methanethioyl radical at the carbon- and nitrogen- end of methanimine, respectively. Natural bond orbital (NBO) analysis at the BHandHLYP/6-311G** level of theory reveals that SOMO-pi*imine, SOMO-piimine, SOMO-LPN and pi*radical-LPN interactions are worth 111, 89, 115 and 17 kJ mol-1, respectively, in the transition state (4) for the reaction of methylimidoyl radical at the nitrogen end of methanimine; similar interactions are observed for the chemistry involving all the radicals studied here. These multi-component interactions are responsible for the unusual motion vectors associated with the transition states involved in these reactions.</p

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

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.</p

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

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.</p

First determination of the rate constant for ring-closure of an azahexenoyl radical: 6-aza-7-ethyl-5-hexenoyl

Competitive kinetic experiments utilising free radical carbonylation chemistry provide a first estimate for the rate constant for 6-endo cyclization of the 6-aza-7-ethyl-5-hexenoyl radical of (4.8 ± 2.4) X 106 s-1 at 90 ° C in benzene, in good agreement with ONIOM-G3(MP2)-CC+COSMO-RS calculations (6.8 X 106 s -1).</p

First determination of the rate constant for ring-closure of an azahexenoyl radical: 6-aza-7-ethyl-5-hexenoyl

Competitive kinetic experiments utilising free radical carbonylation chemistry provide a first estimate for the rate constant for 6-endo cyclization of the 6-aza-7-ethyl-5-hexenoyl radical of (4.8 ± 2.4) X 106 s-1 at 90 ° C in benzene, in good agreement with ONIOM-G3(MP2)-CC+COSMO-RS calculations (6.8 X 106 s -1).</p

Intramolecular homolytic substitution of seleninates: a computational study

Ab initio and density functional theory (DFT) calculations predict that intramolecular homolytic substitution by alkyl radicals at the selenium atom in seleninates proceeds through smooth transition states in which the attacking and leaving radicals adopt a near collinear arrangement. When forming a five-membered ring and the leaving radical is methyl, G3(MP2)-RAD calculations predict that this reaction proceeds with an activation energy (DE 1) of 30.4 kJ mol-1. ROBHandHLYP/6-311++G(d,p) calculations suggest that the formation of five-membered rings through similar intramolecular homolytic substitution by aryl radicals, with expulsion of phenyl radicals, proceeds with the involvement of a hypervalent intermediate. This intermediate further dissociates to the observed products, with overall energy barriers of about 40 kJ mol-1. Homolytic addition to the phenyl group was found not to be competitive with substitution, with a calculated barrier of 57.6 kJ mol-1. This computational study provides insight into homolytic substitution chemistry involving seleninates.</p

7-Selenabicyclo2.2.1heptane

Thermolysis of a benzene solution of N-4-(p-(methoxybenzyl)seleno) cyclohexanoyl-N,S-dimethyldithiocarbonate affords the hitherto unknown 7-selenabicyclo2.2.1heptane in 48% conversion and in 20% yield after chromatography. G3(MP2)-RAD calculations predict a rate constant of 5 X 104 s-1 at 80 °C (3.8 X 106 s -1 at 200 °C) for the intramolecular homolytic substitution process involved in this cyclization.</p