The tetra-alkyl-ammonium halides are electrolytes that have special characteristics due to the presence of hydrocarbon chains.
They have been used asmodel compounds to study hydrophobic interactions due to their fairly large solubility in water and
because of the possibility of change in the length and geometry of the alkyl chains. In this work the solution enthalpies
of tetra-n-butyl-ammonium bromide, tetra-sec-butyl ammonium bromide, tetra-iso-butyl-ammonium bromide and di-n-butyl-di-sec-butyl ammonium bromide were determined at 298.15 K at concentrations between 0.001 and 0.01 mol kg−1. The experimental method used was isoperibol calorimetry. The results were extrapolated fitting the experimental data by
least squares to obtain the solution enthalpies at infinite dilution. The hydrocarbon chains studied were so chosen because
the tetra-n-butyl-ammonium ion is considered to be a structure maker for water. The results show that the geometry of the ion and of
the hydrocarbon chains play an important role in the behavior properties of the solutions.