Enthalpies of formation of nitromethane and nitrobenzene: New experiments vs. quantum chemical calculations

• Thermochemical data for nitromethane and nitrobenzene has been revised.
• New liquid state enthalpies of formation were measured by calorimetry.
• G4 method was applied to derive theoretical gas state enthalpies of formation.
• Consistency of new and available in the literature data has been examined.

Enthalpies of combustion of highly pure nitromethane and nitrobenzene have been measured with precise combustion calorimetry. Enthalpies of vaporisation for both compounds were collected and evaluated. A new, internally consistent experimental data set of ΔfHm°(g) values for nitromethane and nitrobenzene was compared with the results of one of the most accurate first-principles G4 method applied to both atomization and isodesmic reactions. It was shown that the values calculated using the atomization reaction procedure are underestimated by 6.6 kJ · mol−1 for nitromethane and 9.1 kJ · mol−1 for nitrobenzene. An isodesmic reaction scheme strongly supports the internal consistency of new experimental values. A simple “corrected atomization procedure” to derive reliable theoretical enthalpies of formation directly from the G4 atomization reaction values has been tested and recommended as the alternative to the bond separation and isodesmic reactions.