Arturo Ximello - Gas phase enthalpies of formation of nitrobenzamides using combustion calorimetry and thermal analysis

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    • Formation enthalpies of the nitrobenzamides were derived from   combustion calorimetry.  
    • Enthalpies of vaporisation and sublimation were calculated by   thermogravimetry.  
    • From gas phase enthalpies of formation the stability of the   isomers is studied.  
    • Stability of isomers is not driven by a steric hindrance   between functional groups.  


      DOI: 10.1016/j.jct.2014.07.006


        The standard molar energies of combustion of 2-nitrobenzamide,   3-nitrobenzamide and 4-nitrobenzamide were determined with an   isoperibolic, static-bomb, combustion calorimeter. From the   combustion results, the standard molar enthalpies of combustion   and formation for these compounds in the condensed phase   at T = 298.15 K   were derived. Subsequently, to determine the enthalpies of   sublimation, the vapour pressure data as a function of the   temperature for the compounds under investigation were estimated   using thermogravimetry by applying Langmuir’s equation, and the   enthalpies of vaporisation were derived. Standard enthalpies of   fusion were measured by differential scanning calorimetry then   added to those of vaporisation to obtain reliable results for the   enthalpy of sublimation. From the combustion and sublimation   data, the gas phase enthalpies of formation were determined to be   (−138.9 ± 3.5) kJ·mol-1,   (−122.9 ± 2.9) kJ·mol-1 and   (−108.5 ± 3.7) kJ·mol-1 for   the orthometa and para isomers   of nitrobenzamide, respectively. The meaning of these results   with regard to the enthalpic stability of these molecular   structures is discussed herein.

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