ELECTRON SPIN RESONANCE STUDIES OF RADICAL ANIONS AND ION PAIRS IN THE PYRAZINE SERIES

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Abstract
The alkali metal hyperfine interaction in ion pairs of sodium and potassium cations with the radical anions of some methyl-substituted pyrazines and pyridines has been investigated. The electrostatic, electronic, and steric interactions which influence the metal hyperfine splitting are discussed in detail. It is proposed that the variation of the observed hyperfine splitting is due, in some cases, to steric effects, but in the series of m-xylene, 3,5-dimethylpyridine, and 2,6-dimethylpyrazine, the variation is caused by a change in the energy of electronic excitations from the anion to the cation.The results of molecular orbital calculations of the spin densities in tetramethylpyrazine and 3,5-dimethylpyridine are compared with experiment and found to give reasonable agreement.