AMINOALKYL AND ALKYLAMINIUM FREE-RADICALS AND RELATED SPECIES - STRUCTURES, THERMODYNAMIC PROPERTIES, REDUCTION POTENTIALS, AND AQUEOUS FREE-ENERGIES

The structures of H2NCH2+, H2NCH2., H2NCH3, H2NCH3.+, H3NCH2.+, (CH3)2NCH2+, (CH3)2NCH2., (CH3)3N, and (CH3)3N.+ were optimized at the HF/6-31G* and MP2/6-31+G* levels, and the frequencies were calculated at the HF/6-31G* level. For H2NCH2+, H2NCH2., H2NCH3, H2NCH3.+, and H3NCH2.+ the total energies were evaluated at the G2 level and those of (CH3)2NCH2+, (CH3)2NCH2., (CH3)3N, and (CH3)3N.+ at the level of MP2/6-31+G*+ZPE. Where comparisons were possible, heats of formation from these results agreed well with recent literature data. On the basis of the structural information from the ab initio calculations and an analysis of the solution free energies of the parent compounds, solution free energies were calculated for the radicals studied by the G2 procedure and several others for which reliable heats of formation were available. These data were used to obtain values of DELTA(f)G-degrees(aq) and reduction potentials for the R1R2NCR3H. radicals in reaction 2: R1R2NCR3H. + e- + H+ --> R1R2NCR3H2. The values of DELTA(f)G-degrees(aq) for several ionic species were obtained from literature data and used to calculate values of E-degrees(6) for reaction 6: R1R2NCR3H2.+ + e- --> R1R2NCR3H2. Estimates of E-degrees(1) for reaction 1, R1R2NCR3H+ + e- - R1R2NCR3H4., were also obtained. These confirmed the strong reducing character of the alpha-amino radicals. Existing experimental data on aqueous solutions are discussed in the light of the present results.