Structural, energetic and reactivity properties of phenoxazine and phenothiazine

A combined experimental and computational study was developed with the aim of evaluate and understand the structural, energetic and reactivity properties of phenoxazine and phenothiazine. Experimentally, differential scanning calorimetry, static and rotating bomb combustion calorimetries, Knudsen effusion and Calvet microcalorimetry were employed to determine, respectively, the standard (p degrees = 0.1 MPa) molar enthalpies of fusion, Delta H-1(cr)m degrees, at the temperature of fusion, the standard molar enthalpies of formation, in the crystalline phase, Delta H-f(m)degrees(cr), at T = 298.15 K, the temperature-vapor pressures dependences, and the standard molar enthalpies of sublimation, Delta H-g(cr)m degrees, at T = 298.15 K. These data allowed the derivation the experimental standard molar enthalpies of formation, in the gaseous phase, Delta H-f(m)degrees(g), of phenoxazine, (100.8 +/- 4.3) kJ.mol (1), and of phenothiazine, (273.5 +/- 4.7) kJ.mol (1). Computationally, the composite G3(MP2)//B3LYP approach was used to optimize the structures of these two compounds and to estimate their Delta H-f(m)degrees(g) values, which are found to be in very good agreement with the experimental ones. Calculations were also performed for additional analyses of their natural bond orbitals (NBO) and to obtain other gas-phase thermodynamic properties, namely N-H bond dissociation enthalpies, gas-phase acidities and basicities and proton affinities. (C) 2013 Elsevier Ltd. All rights reserved

Energetics and Reactivity of Morpholine and Thiomorpholine: A Joint Experimental and Computational Study

The influence of the heteroatoms in the conformational, energetic, and reactivity trends exhibited by morpholine and thiomorpholine isosteres was obtained from computational and experimental thermochemical studies. For those purposes, the gas-phase standard (p = 0.1 MPa) molar enthalpies of formation of the compounds, at T = 298.15 K, were determined from the experimental values of the standard molar. enthalpies of formation, in the liquid phase, and of the standard molar: enthalpies of vaporization, obtained by calorimetric techniques, and also from composite G3(MP2)// B3LYP calculations making use of appropriate working reactions. A very good agreement was found between the calculated and the experimental gas-phase enthalpies of formation. The computational study was further extended to the calculation of other gas-phase thermodynamic properties these compounds, namely, the N-H or C-H bond dissociation enthalpies, gas-phase acidities and basicitics, proton affinities and adiabatic ionization enthalpies, and the energies and structures of the conformational stereoisomers of morpholine and thiomorpholine