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Development of the method used by Benson's group for estimating enthalpies of vaporization permits calculation of the enthalpies of formation of the following classes of organic compound in the liquid phase: alkanes, cycloalkanes, alkenes, chloro- and bromoalkanes, alcohols, acids, aldehydes, esters, nitriles, aromatic hydrocarbons, and mercaptans. For high polarity molecules, some correction terms must be introduced into the calculation.

In our previous publications it has been shown that the method of Benson's group permits the estimation of the enthalpies of vaporization of organic compounds. In the present paper we have applied this method for unsaturated hydrocarbons, thus completing our previous work on acyclic alkenes. For the alkylbenzenes we have changed the values of the groups C-(C b )(C)(H) 2 and C-(C b )(C) 2 (H) previously determined. A more accurate value for the enthalpies of vaporization of the alkylbenzenes of higher molecular weight is obtained.

In a recent publication it was shown that the method of Benson's group permitted the estimation of the enthalpies of vaporisation for organic monofunctional compounds. The present paper includes molecules of the type R 1 —X—R 2 with X = O, S, CO, and primary, secondary and tertiary amines. Calculations are also reported for mono- and disubstituted derivatives of 1,2 dihydroxyethane and acetals.

Solution enthalpies of acetic, propionic and isobutyric acid in water and in mixtures of water and t-butylalcohol are drawn from calorimetric measurements. For those three acids, enthalpies of transfer from water to the hydroorganic solvents exhibit a maximum for a particular composition of the solvents. These results are discussed in terms of structure of the hydroalcoholic media and of structure-breaking and -making abilities of the solutes.