Translational diffusion of chemically stable and reactive radicals in solution

Translational diffusion constants (D) of chemically stable radicals (TEMPO, its derivatives and DPPH) and their analogous non-radicals (closed-shell molecules) have been investigated by the Taylor dispersion method. It has been found that TEMPO and its derivatives diffuse more slowly than the closed-shell molecules with similar molecular sizes and shapes in alcoholic solvents. On the other hand, in aprotic and nonpolar solvents, the D values of TEMPO and the closed-shell molecules are similar. D for DPPH is close to that of the closed-shell molecule with the same size. A chemically reactive radical of a similar structure is created by the photoinduced hydrogen abstraction reaction of tetramethylcyclohexanone in ethanol, and D values for the radical and the parent molecule are measured by the transient grating method. D values for the chemically reactive and stable radicals are compared.