Diaminobenzenes: An Experimental and Computational Study

In the present work, the values of the standard (p o = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of 1,2-diaminobenzene, 1,3-diaminobenzene, and 1,4-diaminobenzene are reported as 86.6 ± 1.6, 89.6 ± 1.6, and 99.7 ± 1.7 kJ·mol−1, respectively. These values were derived from experimental thermodynamic parameters, namely the standard (p o = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, Δf H m o(cr), at T = 298.15 K, obtained from the standard molar enthalpies of combustion, Δc H m o, measured by static bomb combustion calorimetry, and the standard molar enthalpies of sublimation, at T = 298.15 K, derived from the temperature-vapor pressure dependence, determined by the Knudsen mass loss effusion method. The results were compared with estimates obtained by standard ab initio molecular calculations at the G3(MP2)//B3LYP level. Experimental and calculated data are in very good agreement and show that the 1,2-diaminobenzene is, thermodynamically, the most stable isomer. Finally, proton and electron affinities, basicities and adiabatic ionization enthalpies were also computed at the same level.