Destabilization in the isomeric nitrobenzonitriles: An experimental thermochemical study

The enthalpies of combustion and of sublimation, respectively, of the three isomeric nitrobenzonitriles have been measured: o-, {(−3456.3±2.9), (88.1±1.4)} kJ·mol−1; m-, {(−3442.8±3.3), (92.8±0.3)} kJ·mol−1; p-, {(−3448.2±3.6), (91.1±1.3)} kJ·mol−1. In turn, from these values, the standard molar enthalpies of formation for the condensed and gaseous state, respectively, have been derived: o-, {(130.1±3.1), (218.2±3.4)} kJ·mol−1; m-, {(116.5±3.5), (209.3±3.5)} kJ·mol−1; p-, {(122.0±3.8), (213.1±4.0)} kJ·mol−1. Destabilization energies associated with the presence of the two electron-withdrawing groups have been determined, for o-, m-, and p-nitrobenzonitrile, {(17.6±4.1), (8.7±4.2), and (12.5±4.6)} kJ·mol−1, respectively, and are consistent with those obtained for the corresponding sets of isomeric methyl benzenedicarboxylates, dicyanobenzenes, dinitrobenzenes, and (neutral and ionized) nitrobenzoic acids.The support of the Spanish DGI under Project BQU2000-1497 is gratefully acknowledged. M.T. thanks CSIC (I3PBPG2001), Spain, for financial support