Unstable intermediates. Part LVI. An electron spin resonance study of the radicals formed by γ-irradiation of pyridine and some of its derivatives

Abstract

The e.s.r. spectrum of the radical formed by exposure of pyridine to γ-rays at 77°K is assigned to the 2-pyridyl radical. The magnetic properties show that the unpaired electron's orbital, which is formally sp² on carbon, in fact includes a large contribution from the sp² lone-pair orbital on the adjacent nitrogen atom, making this radical structurally similar to benzyne. On warming, the radical adds to another pyridine molecule. The relationship between these radicals and others that can be obtained from pyridine and pyridinium ions is discussed.