Proton Magnetic Resonance in Organic Free Radicals, BDPA–Bz and p-Cl-BDPA

Abstract

The proton NMR absorption spectra from 1.3 to 77 K in two organic free radicals, BDPA–Bz and p-Cl-BDPA, have been measured on powder samples which undergo a magnetic phase transition from a paramagnetic to an antiferromagnetic state at the temperatures of 1.695 and 3.25 K respectively. The behavior of the NMR absorption spectra associated with the magnetic phase transition has been studied for the first time in the organic free radicals and interpreted in terms of the hyperfine interaction. These results are then compared with those of the TANOL radical, which is a linear antiferromagnet with no magnetic phase transition down to 1.3 K.