The equilibrium constants K for the ketoreductase-catalyzed reduction reactions (2-substituted cyclohexanone + 2-propanol = cis-and trans-2-substituted cyclohexanol + acetone) have been measured in n-hexane as solvent. The 2-substituted cyclohexanones included in this study are: 2-methylcyclohexan one, 2-phenylcyclohexanone, and 2-benzylcyclohexanone. The equilibrium constants K for the reactions with 2-methylcyclohexanone were measured over the range T = 288.15 to 308.05 K. The thermodynamic quantities at T = 298.15 K are: K = (2.13 +/- 0.06); Delta(r)G(m)(o) = -(1.87 +/- 0.06) kJ center dot mol(-1); Delta H-r(m)o = -(6.56 +/- 2.68) kJ center dot mol(-1); and Delta S-r(m)o = -(15.7 +/- 9.2) J center dot K-1 center dot mol(-1) for the reaction involving cis-2-methylcyclohexanol, and K=(10.7 +/- 0.2); Delta(r)G(m)(o)=-(5.87 +/- 0.04) kJ center dot mol(-1); Delta H-r(m)o = -(2.54 +/- 1.8) kJ center dot mol(-1); and Delta S-r(m)o = (11.2 +/-6.4) J center dot K-1 center dot mol(-1) for the reaction involving trans-2-methylcyclohexanol. The standard molar Gibbs free energy changes Delta(r)G(m)(o) for the reactions (trans-2-substituted cyclohexanol = cis-2-substituted cyclohexanol) in n-hexane have also been calculated and compared with the literature data that pertain to reactions in the gas phase and at higher temperatures. Experiments carried out with a chiral column demonstrated that the enzymatic reduction of 2-phenylcyclohexanone catalyzed by the ketoreductase used in this study is not stereo selective. (C) 2006 Elsevier Ltd. All rights reserved.