Molecular orbital calculations of the ionization potentials and stabilization energies of aminoalkyl radicals

Abstract

A series of aminoalkyl radicals, H2NCH2, H(CH3)NCH2, (CH3)2NCH2, H2NC(CH3)H, H2NC(CH3)2, and the corresponding amines have been examined by abinitio computations. The first vertical ionization potentials of the radicals calculated by the direct SCF method were very low: H2NCH2 (6.3 eV), H(CH3)NCH2 (6.0 eV), and (CH3)2NCH2 (5.8 eV) and decreased with methyl substitution at nitrogen. The first ionization potentials of H2NC(CH3)H and H2NC(CH3)2 were predicted to be 5.9 and 5.6 eV respectively. Radical stabilization energies were calculated from SCF results in several basis sets and with several choices of optimized geometries for R2NCR2 + CH4 → R2NCR2H + CH3. The aminomethyl radical, H2NCH2, was calculated to be 8 to 10 kcal/mol stabilized relative to methyl. The present calculations predict that methyl substitution at N has a small destabilizing effect onH2NCH2 which contrasts with recent experiments. The effect of methyl substitution and details of the "three-electron" bond in aminoalkyl radicals are examined qualitatively by orbital interaction diagrams.