Pyridine Anion Research Articles

The Electron Spin Resonance and Electronic Spectra of 4-Substituted Pyridinyl Radicals

Abstract The ESR and electronic absorption spectra have been measured with the 1-methyl-4-carbo-methoxy-, 1-methyl-4-carbamido-, 1-methyl-4-acetyl- and 1-methyl-4-cyanopyridinyl radicals. From the analysis of their ESR spectra by the aid of a spectrum accumulator, we have been able to determine the nitrogen and hydrogen hyperfine splitting constants of these pyridinyl radicals, from which the spin distributions have then been evaluated. These radicals except for the 1-methyl-4-carbamidopyridinyl radical, have been found to show three absorption bands, at 300–350 mμ, at about 400 mμ and at about 600 mμ. From the results of the ESR and electronic absorption spectra, the electronic structures of these pyridinyl radicals have been concluded to be similar to those of the 4-substituted pyridine anion radicals. The preparation of 1,2,6- and 1,3,5-trimethyl-4-substituted pyridinyl radicals has been attempted. The latter radicals, except for the 1,3,5-trimethyl-4-cyanopyridinyl radical, were not detected by the ESR and electronic absorption spectra, because the steric hindrance of the methyl groups at the 3 and 5 positions prevents them from achieving the resonance stabilization due to the 4-substituent.

The Electron Spin Resonance and Electronic Spectra of the Anion Radicals of 4-Nitropyridine and 4-Nitropyridine 1-Oxide

Abstract The ESR and electronic spectra of the 4-nitropyridine and 4-nitropyridine 1-oxide anions have been measured. The nitrogen and hydrogen hyperfine splitting constants of these two compounds have been determined. In order to analyze the ESR spectra exactly, the measurements have also been carried out with respective compounds containing 15N instead of 14N in the nitro group. The spin densities on the nitrogen and carbon atoms of these two anions have been estimated from the splitting constants. It has thus been found that the spin densities on the ring nitrogen and carbon atoms are undoubtedly larger in the 4-nitropyridine 1-oxide anion than in the 4-nitropyridine anion. The electronic spectrum of the 4-nitropyridine anion has been measured and three peaks found at 313, 440 and 640 mμ. According to the molecular orbital calculations carried out with the π-electron system of the 4-nitropyridine anion, it has been concluded that the 440 mμ band may be regarded as the intramolecular charge transfer band, and that the 313 mμ band can be interpreted as the blue shifted band of the pyridine anion.