Signs of the Isotropic Hyperfine Splittings in the Electron Spin Resonance Spectrum of the Dihydropyrazine Cation Radical

Abstract

Linewidth studies of the electron spin resonance spectrum of the dihydropyrazine cation radical have been employed to determine the signs of the isotropic hyperfine splittings. It was found that the nitrogen splitting a^N is positive and the proton splitting a_NH^H of the protons bonded to the nitrogen atoms is negative. The sigma—pi parameter Q_NH^H in McConnell's relation for NH bonds (a_NH^H=Q_NH^HρN^π) was found to be negative.