AbstractVolumes of activation, ΔV≠, and reaction, ΔV, partial molar volumes, $\bar{V}$, and enthalpies of solution, ­ΔsolH, were determined for tetracyanoethylene, cyclopentadiene, 1,3‐butadiene, trans, trans‐1,4‐diphenyl‐1,3‐butadiene and their Diels–Alder adducts at 25 °C in some solvents of π‐ and n‐donor type. The values of the activation and reaction volumes were exceptionally small in the former type of solvents. Large solvent effects on ΔsolHTCNE (up to 26 kJ mol−1), $\bar{V}$TCNE, ΔV and ΔV≠ (up to 11 cm3mol−1) were observed in aromatic solvents and these values are linearly correlated with each other. Poor correlations were found for n‐donor solvents, but a linear dependence between ΔV and δr−nH (enthalpy of reaction) was obtained for all solvents. Copyright © 2001 John Wiley & Sons, Ltd.