THEORETICAL INVESTIGATION OF SPIN-TRAPPING REACTIONS

The energetics of spin-trapping and related reactions, using nitrosomethane as a model spin trap, are examined using quantum chemical calculations at the MP2/6-31+G* level. It is established that nitrosomethane is a satisfactory model for the commonly employed spin trap 2-methyl-2-nitrosopropane. Free energy differences are reported for the reactions considered, using theoretically determined molecular structures and vibrational frequencies to convert molecular energies to room-temperature free energies. The effects of solvation are estimated by means of a self-consistent reaction field approach. The level of theory applied here is not expected to be quantitatively predictive, but it is expected to be of value in establishing energetic trends among possible reactions. Results reported here indicate that nitrosomethane dimer and the anion of the monomer are capable of reacting as spin traps, although less effectively than the monomer. In all cases, the ultimate product appears to be the nitroxide.