of sodium, lithium, barium, and magnesium perchlorate in acetone solution on the rates of different Diels-Alder reactions were kinetically investigated, 13 C-NMR spectroscopy being used as a tool to infer the mechanism of coordination of the solvated cations acting as catalysts. The Diels-Alder reactions, whose rates increase with increasing electrophilic character of the solvent, are strongly accelerated