HYDROGEN-BOND FORMATION AND MOLECULAR-MOTION IN SOLUTIONS OF ANILINE WITH NITROXIDE FREE-RADICALS

1H NMR spin-lattice relaxation rates and paramagnetic contact shifts have been measured at various temperatures and frequencies in solutions of aniline, aniline-d2, and aniline-d5 containing nitroxide free radicals. The data can be explained in terms of transient hydrogen bond formation between the amino protons and the NO groups of the radical. Detailed information about the intermolecular transfer of electron spin density and the steric arrangement of the complex have been obtained. Molecular motions and interactions have been probed by relaxation measurements over a large frequency range between 100 kHz and 300 MHz. The results are compared with other hydrogen-bonded complexes of nitroxide radicals and proton donor solvent molecules.