A series of Cu(II)-63 dithiocarbamates with alkyl and cycloalkyl substituents of various shape, size and rigidity has been prepared. Their rotational correlation times (Ƭ₂) were measured (in the fast motional regime) in toluene using the line-widths of their ESR spectra. The ESR spectra were recorded on paper tape with a digital acquisition system and analysed on an Amdahl 470 computer utilising specially written programs. This procedure results in a substantial improvement in precision over earlier manual methods. The observed correlation times were compared with those calculated by the QLRF model, the conditional free rotation model, the Stokes-Einstein and Perrin 'stick' hydrodynamic models and the 'slip' hydro- -dynamic model. The results in relation to Pecora's extension of the hydrodynamic model are also discussed. The statistical mechanical and 'stick' hydrodynamic models proved unsatisfactory. The results are adequately described by the 'slip' hydrodynamic model with an additional term ascribable to a free-rotation correlation time (Ƭ₀); i.e. Ƭ₂ = Cn + Ƭ₀ ¯¯¯ Ƭ where n is the viscosity of the solvent and C is a function of the size and shape of the molecule calculated from the ' slip ' theory. / Science, Faculty of / Chemistry, Department of / Graduate