Thermodynamic properties of methylquinolines: Experimental results for 2,6-dimethylquinoline and mutual validation between experiments and computational methods for methylquinolines

Measurements leading to the calculation of the standard thermodynamic properties for gaseous 2,6-dimethylquinoline (Chemical Abstracts registry number [877-43-0]) are reported. Experimental methods included adiabatic heat-capacity calorimetry, vibrating-tube densimetry, comparative ebulliometry, inclined-piston gauge manometry, differential-scanning calorimetry (d.s.c.), and combustion calorimetry. The critical temperature was measured with d.s.c. The critical pressure and critical density were estimated. Molar entropies, molar enthalpies, and molar Gibbs free energies of formation for the ideal gas state were derived at selected temperatures between 298.15 K and 700 K. Results are compared with experimental property values reported previously in the literature. Independent calculations of the ideal gas entropies were performed at the B3LYP/6-31+G(d,p) model chemistry for 2,6-dimethylquinoline and other methylquinolines (including hindered internal rotations) and are shown to be in excellent accord with the calorimetric results. Implications of these results are discussed.