Chemical Processes Subsequent tonmdash;pgr;*and pgr;mdash;pgr;*Transitions of PyridineNhyphen;oxide and 2hyphen;PicolineNhyphen;oxide

摘要

The gaseous photolysis of pyridineNhyphen;oxide was carried out by irradiating with the 3261 A (Cd) or 2537 A (Hg) resonance line which corresponds to the absorption due to annmdash;pgr;*or a pgr;mdash;pgr;*transition of this substance, respectively. The main product was pyridine in both cases. However, there exists a remarkable difference in the relation between the quantum yield of pyridine produced and the temperature. In the case of 3261 A irradiation the quantum yield of pyridine increases steeply at temperatures greater than 80deg;C, which means that an activation energy would be required for the production of pyridine. On the other hand, the quantum yield of pyridine produced at 2537 A irradiation was nearly independent of the temperature. The activation energy necessary for the production of pyridine in the case of 3261 A irradiation is about 11.9 kcal molmdash;1, which was estimated from the temperaturehyphen;dependence of the quantum yield of pyridine. The chemical processes succeeding to annmdash;pgr;*or a pgr;mdash;pgr;*transition of pyridineNhyphen;oxide were interpreted under the assumption that the excited molecule dissociates to pyridine and atomic oxygen in a predissociative manner, in which a triplet state crossing with the first excited state exists as a shorthyphen;lived intermediate.The gaseous photolysis of 2hyphen;picolineNhyphen;oxide was also carried out by irradiating it with the 3261 or 2537 A resonance line. It was found that 2hyphen;picolineNhyphen;oxide undergoes a photochemical rearrangement to isomerize to 2hyphen;pyridinemethanol at 3261 A (nmdash;pgr;*transition) and a fission of Nrarr;O bond to produce 2hyphen;picoline at 2537 A (pgr;mdash;pgr;*transition).