Energetics of the N-O bonds in 2-hydroxyphenazine-di-N-oxide

The standard enthalpy of formation and the enthalpy of sublimation of crystalline 2-hydroxyphenazine-diN-oxide, at T = 298.15 K, were determined from isoperibol static bomb combustion calorimetry and from Knudsen effusion experiments, as -76.7 +/- 4.2 kJ center dot mol(-1) and 197 5 kJ center dot mol(-1), respectively. The sum of these two quantities gives the standard enthalpy of formation in the gas-phase for this compound, Delta(f)H(m)degrees(g) = 120 6 KJ center dot mol(-1). This value was combined with the gas-phase standard enthalpy of formation for 2-hydroxyphenazine retrieved from a group estimative method yielding the mean (N-O) bond dissociation enthalpy, in the gas-phase, for 2-hydroxyphenazine-di-N-oxide. The result obtained with this strategy is = 263 +/- 4 KJ center dot mol(-1), which is in excellent agreement with the B3LYP/6-311+G(2d,2p)// B3LYP/6-31G(d) computed value, 265 KJ center dot mol(-1)

A Combined Experimental and Computational Thermodynamic Study of Difluoronitrobenzene Isomers

This work reports the experiunental and computational thermochemical study performed on time dilluorinated nitrobenzene isomers: 2,4-dilluoronitrobenzene (2,4-DFNB), 2,5-di fluoronitrobenzene (2.5-DFN13), and 3,4difluoronitrobenzene (3.4-DFNI3). The standard (p(o) = 0.1 WIN) molar enthalpies of formation in the liquid phase of these compounds were derived from the standard molar energies of combustion, in oxygen, at 7' = 298.15 K, measured by rotating bomb combustion ealorimetry. A static method was used to perform the vapor pressure study of the referred compounds allowing the construction of the phase diagrams and determination of the respective triple point coordinates, as well as the standard molar enthalpies of vaporization, sublimation, and fusion for two of the isomers (2,4-DFN13 and 3,4-DFN113). For 2,5-dilluoronitrobenzene, only liquid vapor pressures were measured enabling the determination of the standard molar enthalpies of vaporization. Combining the thermodynamic parameters of the compounds studied, the following standard (p(o) = 0.1 MN) molar enthalpies of formation in the gaseous phase, at T = 298.15 K, were derived: Delta(f)H(m)(o)(2,4-DFNB, g) = (296.3 +/- 1.8) kJ.mol(-1), Delta(f)H(m)(o)(2,5-DFNB, g) = (288.2 +/- 2.1) kJ.mol(-1), and Delta(f)H(m)(o)(3,4-DFNB, g) = -(302.4 +/- 2.1) kJ.mol(-1). Using the empirical scheme developed by Cox, several approaches were evaluated in order to identify the best method for estimating the standard molar gas phase enthalpies of.formation of these compounds. The estimated values were compared to the ones obtained experirrientally, and the approach providing the best comparison with experiment was used to estimate the thermodynamic behavior of the other difluorinated nitrobenzene isomers not included in this study. Additionally, the enthalpies of formation of these compounds along with the enthalpies of formation of the other isomers not studied experimentally, i.e., 2,3-DFNB, 2,6-DFNB, and 3,5-DFNB, were estimated using the composite G3MP2B3 approach together with adequate gas-phase working reactions. Furthermore, we also used this computational approach to calculate the gas-phase hasicities, proton and electron affinities, and, finally, adiabatic ionization enthalpies