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. (C) 2003 Elsevier Science Ltd. All rights reserved.