Electron spin resonance spectra of the radical anions of pyridine and related nitrogen heterocyclics

The E.S.R. spectra of the radical anions of pyridine, 4-picoline, 3,5-lutidine, 2,6-lutidine, pyrazine, pyrimidine, pyridine N-oxide, 4-picoline N-oxide and 2,6-lutidine N-oxide have been observed in liquid ammonia. The data for pyridine, pyrazine and pyrimidine can be combined to evaluate Q N N = +27·3, Q CN N = -1·7 and Q H = -24·5 gauss independently of molecular orbital spin densities. Good agreement is found for the observed coupling constants for the N-heterocyclics and McLachlan's theory with methyl group coupling consistent with both Levy's hyperconjugation equations and with Q CH3 eff. = 25·7 gauss. The coupling constants for the N-oxides are in satisfactory agreement with an arbitrary set of molecular orbital parameters.