Enthalpies of interaction of alkanes and alkenes with polar and nonpolar solvents

Abstract

Enthalpies of solution (AHS) of a variety of straight-chain, branched, and cyclic alkanes and alkenes have been measured in methanol, TV.iV-dimethylformamide (DMF), benzene, and cyclohexane. AHS values and enthalpies of evaporation {AHV) have been combined to give enthalpies of transfer from the vapor to each solvent [ //( -S)]. These solvation enthalpies are more exothermic for alkenes than for the corresponding alkanes in transfers to methanol, DMF, and benzene, by about 0.3, 0.6, and 0.3 kcal/mol, respectively, but are similar in transfers to cyclohexane. This suggests that solute-solvent interactions in cyclohexane are mainly dispersion forces. The more exothermic interaction of DMF with alkenes relative to alkanes results mainly from dipole-induced dipole interactions of the solvent dipoles with the highly polarizable bonds. Only very large steric factors inhibit the approach of solvent dipoles to the tr bond, as in trans-1,2-di-terr-butylethylene, where the alkene-alkane difference in AH(v -* S) is diminished. AH(v -* S) of alkanes and alkenes are reduced by nearly l kcal/mol for each quaternary carbon atom present, possibly arising from steric hindrance to solvation by dispersion forces.

Synthesis and solution properties of gemini surfactants containing oleyl chains

“…While a more exothermic value is expected because of the longer hydrocarbon chain length in the former series, the difference turns out to be far less negative per -CH 2 -group than the À1.6 kJ mol À1 of -CH 2 -found for many single-head, single-tail surfactants. 38 However, since a carbon-carbon double bond is more hydrophilic than a carbon-carbon single bond, 39 this could give rise to a less exothermic DH1 M for the unsaturated compared to the saturated hydrocarbon chain systems. Conformational differences between the unsaturated and saturated carbon chains are also likely to contribute to the reduced exothermic nature of the self-aggregation process.…”

Enthalpies and heat capacities of solution for tert-butyl chloride and bromide in alcohols. Application of SPT, SRMR, and MS

“…be of main interest to obtain more calorimetric data for model hydrocarbons, specially gaseous ones, in a larger variety of solvents and at different temperatures (18,23).…”

Heats of vaporization of monoalkylcyclohexanes by the gas chromatography – calorimetry method

“…The vacuum jacketed calorimeter (volume 100 mL) containing 50 mL of DC-200 was stirred with a commercial magnetic bar (12 x 37 mm) using a stirring unit within the constant temperature bath (25.00 k 0.001'C) powered by a 300 rpm constant speed gear motor. Even with this increased stirring a somewhet longer period of time (2-3 min) was required to reach the final baseline (following sample addition or operation of the calibration heater) than is required with less viscous solvents (5,25). However, improved sensitivity (200 pV full scale recorder deflection) compared with a previous report (15) …”

“…Heats of solution of the calibration compounds and the alkylcyclohexanes were determined in DC-200 silicone fluid with apparatus slightly modified from that previously described (5,15,25). The vacuum jacketed calorimeter (volume 100 mL) containing 50 mL of DC-200 was stirred with a commercial magnetic bar (12 x 37 mm) using a stirring unit within the constant temperature bath (25.00 k 0.001'C) powered by a 300 rpm constant speed gear motor.…”

“…It has been applied to liquid substances boiling between 65 and 360°C (5,15), and both lower and higher boiling substances could undoubtedly be handled. Sample size is small (<200-300 pL), and partial decomposition at high temperatures does not affect the results.…”