Calorimetric investigation of the interactions of some hydrogen-bonded systems at 298.15 K

The purpose of this work is to compare the enthalpies of hydrogen-bonded interactions involving a variety of proton donors and accepters. Excess molar enthalpies H-m(E), as a function of mole fraction, are presented for single hydrogen-bonded systems involving propan-1-ol + dipropyl ether, + tripropylamine, + dipropyl sulfide, and + heptan-4-one, dipropylamine + dipropyl ether, + tripropylamine, + dipropyl sulfide, and + heptan-4-one, and propane-l-thiol + dipropyl ether, + tripropylamine, + dipropyl sulfide, and + heptan-4-one. Partial molar enthalpies at infinite dilution H-i,m(E)(x(i)=0), calculated from an analysis of the data near x(i)=0, were used in an attempt to determine the relative strengths and propensities of the hydrogen-bonded interactions OH ... O, OH ... N, OH ... S, NH ... O, NH ... N, NH ... S, SH ... O, SH .. N, and SH ... S. The component molecules are all fully propylated, thus localizing the source of the hydrogen-bonded interaction. For the systems involving a strong hydrogen donor, i.e., alkanol, the liquid phase hydrogen bond strength order mirrors that calculated for interactions in the gas phase from ab initio molecular orbital theory. In the systems involving a relatively weak hydrogen donor, i.e., secondary amine and a thiol, the hydrogen bond strength appears to be related to the available surface area of the hydrogen acceptor atom.