The epr spectra at various frequencies of copper(II) acetate anhydrous, monohydrate, monoacetic acid, and water – acetic acid adduct are presented and analysed. The presence of copper hyperfine splittings in the solid state epr spectra of this series of compounds is discussed. The frozen solution spectrum of copper(II) acetate in acetic acid solution containing ~2% water shows an exceptional resolution ofhyperfine of 24 G. This is attributed to a key intermediate which explains the monomer–dimer dissociation mechanism. The influence of distortions on the structures of these compounds is presented.