Benchmark Thermodynamic Properties of Methyl- and Methoxybenzamides: Comprehensive Experimental and Theoretical Study

The enthalpies of formation of 2-, 3-, and 4-CH₃-benzamide, as well as for 2-CH₃O-benzamide, were measured by using combustion calorimetry. Vapor pressures of the isomeric CH₃- and CH₃O-benzamides were measured by using the transpiration method. The enthalpies of sublimation/vaporization of these compounds at 298 K were obtained from temperature dependencies of vapor pressures. The enthalpies of solution of the isomeric CH₃- and CH₃O-benzamides were measured with solution calorimetry. The enthalpies of sublimation of m- and p-substituted benzamides were independently derived with help of a solution calorimetry-based procedure. The enthalpies of fusion of the CH₃-benzamides were derived from differential scanning calorimetry measurements. Thermochemical data on CH₃- and CH₃O-benzamides were collected, evaluated, and tested for internal consistency. A simple incremental procedure was suggested for a quick appraisal of vaporization enthalpies of substituted benzamides. The high-level G4 quantum-chemical method was used for mutual validation of the experimental and theoretical gas-phase enthalpies of formation. A remarkable ability of the G4-based atomization procedure to calculate reliable enthalpies of formation was established for the set of aliphatic and aromatic amides. An outlook for the proper validation of the G4-AT procedure was discussed

Building Blocks for Ionic Liquids: Vapor Pressures and Vaporization Enthalpies of N‑Functionalized Imidazoles with Branched and Cycloalkyl Substituents

The imidazole structure offers a versatile means of developing molecules with controlled/tunable physicochemical properties that have significant utility in many applications and can be further derivatized to form ionic liquids. In the literature, the vast majority of studies on structure–property relationships in these types of molecules are devoted to linear (e.g., <i>n</i>-alkyl) substituents. However, imidazoles with branched or cycloalkyl groups are equally accessible through convenient synthetic methods – yet there are essentially no reports on the physical properties of such compounds in the literature. Here, the absolute vapor pressures of branched and cycloalkyl derivatives of imidazole have been determined as a function of temperature by the transpiration method. The standard molar enthalpies of vaporization were derived from the temperature dependences of vapor pressures. The measured data sets were successfully checked for internal consistency by comparison with vaporization enthalpies of the parent species, and a group contribution method is put forth by which the vaporization enthalpies of imidazoles, and imidazolium-based ILs, with alkyl groups in any configuration can be rapidly predicted