A method is proposed for relating the thermodynamic functions of hydration ΔXâ– h,c(X=H,G,S), corresponding to the isothermal transfer of an ideal gas at a given molar concentration to an ideal aqueous solution at the same molar concentration, with the molecular structure. In such a method a distinction is made between a constant quantity, χx, related to the general transfer process of a molecule into water and quantities which are determined by the interactions of water with the hydrocarbon backbone, ΔXâ– h,c(R), or with the hydrophilic groups, ΔXâ– h,c(Y). In the case of bifunctional compounds one additional parameter δXâ– h,c(Y1, Y2, rY1–Y2 ) is introduced to account for the interactions between the hydrophilic centres. The quantities χX and ΔXâ– h,c(R) are calculated assuming a linear relationship between the thermodynamic functions of hydration of hydrocarbons or of their radicals and the surface area they expose to the solvent. The quantities ΔXâ– h,c(Y) are calculated from the experimental ΔXâ– h,c(RY) data assuming that the hydrophilic group in RY compounds interacts with water independently of the hydrocarbon backbone R. Finally, the parameters δXâ– h,c(Y1, Y2, rY1–Y2 ) are calculated as excess quantities by comparing the experimental ΔXâ– h,c(RY1Y2) data with those calculated for a hypothetical compound RY1Y2 in which the two hydrophilic centres Y1 and Y2 and the hydrocarbon backbone R interact with water independently of each other. The results show some interesting features of the aqueous solutions of saturated organic compounds such as: (i) the ΔGâ– h,c(Y) contributions to the free energy of hydration in monofunctional compounds are always negative and feebly dependent on the nature of Y. The contrary occurs for the ΔHâ– h,c(Y) and ΔSâ– h,c(Y) quantities which are instead dependent on the nature of Y. (ii) the ΔSâ– h,c(Y) values are always negative and generally much larger in magnitude than the value of the entropy of hydration of the methylene group; (iii) the interactions between polar centres produce positive and almost constant values of δGâ– h,c(Y1, Y2, rY1–Y2 ). However, the enthalpic and entropic parameters connected with the Y1…Y2 interactions in water are strongly dependent on the nature of Y1 and Y2 thus indicating unusual and unpredictable interactions between hydrophilic centres in polyfunctional compounds.