Temperature-dependent hyperfine coupling constants in electron spin resonance. Part 6.—Planar and non-planar nitroxide radicals

Abstract

The coupling constant to ¹⁴N in di-t-butyl nitroxide has a temperature coefficient which is negative and which decreases with increasing temperature. It is argued that the source of this temperature dependence is out-of-plane, or umbrella, vibrations about the non-planar nitrogen centre. Measurements of da^N/dT have also been made for a series of nitroxides having well-defined geometries.