Thermochemistry of 2,2′-dipyridil N-oxide and 2,2′-dipyridil N,N′-dioxide. The dissociation enthalpies of the N−O bonds

In this paper, the first, second and mean (N−O) bond dissociation enthalpies (BDEs) were derived from the standard (p° = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, ΔfHm∘(g), at T = 298.15 K, of 2,2′-dipyridil N-oxide and 2,2′-dipyridil N,N′-dioxide. These values were calculated from experimental thermodynamic parameters, namely from the standard (p° = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, ΔfHm∘(cr), at T = 298.15 K, obtained from the standard molar enthalpies of combustion, ΔcHm∘, measured by static bomb combustion calorimetry, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined from Knudsen mass-loss effusion method.

Research highlights
► The standard enthalpies of formation of two crystalline 2,2´-dipyridil N-oxides were measured by combustion calorimetry.
► The standard enthalpies of sublimation of two 2,2´-dipyridil N-oxides were derived from Knudsen effusion experiments.
► First, second and mean (NO) bond dissociation enthalpies (BDEs) for 2,2´-dipyridil N,N´-dioxide were derived.
► The (NO) bond dissociation enthalpy (BDE) for 2,2´-dipyridil N-oxide was calculated.