Time- and temperature-resolved infrared absorption spectroscopy is used to monitor the ligand substitution reaction of W(CO)(5)(cyclohexane) with a series of ligands L of the form cyclo-C4HnO (n = 4, 6, 8). Second-order rate constants for the formation of W(CO)(5)(L) are obtained over the temperature range 20-60 degreesC, and from these temperature-dependent rare constants, activation parameters for the ligand substitution reaction are obtained. We find that for L = furan, DeltaH(double dagger) = 7.1 +/- 0.7 kcal mol(-1) and DeltaS(double dagger) = -7.1 +/- 5.1 eu; for L = 2,3-dihydrofuran, DeltaH(double dagger) = 5.9 +/- 0.5 kcal mol(-1) and DeltaS(double dagger) = -8.9 +/- 7.3 eu; and for L = 2,5-dihydrofuran, DeltaH(double dagger) = 3.8 +/- 0.2 kcal mol(-1) and DeltaS(double dagger) = -14.0 +/- 3.5 e.u. We find that as L becomes less strongly electron-donating, as determined by the trans C-O stretching force constant of W(CO)(5)L, DeltaH(double dagger) rises and DeltaS(double dagger) becomes less negative. The correlation of the activation enthalpy with the properties of the products and the low activation enthalpies relative to the (CO)(5)W-cyclohexane bond dissociation energy are consistent with an associative interchange (I-a) mechanism for the ligand exchange.