ESR Study of Irradiated Pyridine

Pyridine and pyridine-d5 were irradiated with electrons in the solid state at −196°C. After the irradiation, ESR spectra were measured over a temperature range from −196°C to their melting points. For pyridine, a triplet spectrum (separation of 30 G) with a quartet substructure (separation of 4.3 G) was observed at −196°C. It was assigned to cation radicals[Complex chemical formula]The triplet spectrum disappeared at elevated temperatures and an eight-line spectrum (separation of 12 G) was observed at −90°C which was assigned to free radicals[Complex chemical formula]After the disappearance of these radicals at −65°C, a singlet spectrum (ΔHmsl of 15 G) was observed and disappeared at about −50°C. It was assigned to pyridyl radicals. The radicals produced in the irradiated pyridine-d5 had the same nature as those observed in irradiated pyridine.