Thermochemical Estimation of Destabilization Energies of 1,2-, 1,3-, and 1,4-Dicyanobenzenes Due to Interactions between Substituents. Appendix: Dipole Moments in Solution of the Dicyanobenzenes

Abstract

Abstract Enthalpies of combustion of 1,2-, 1,3-, and 1,4-dicyanobenzenes were determined by precision oxygen-bomb calorimetry. Enthalpies of sublimation of these compounds were obtained by the measurement of temperature dependence of vapor pressure. The standard enthalpies of combustion ΔHc°(298.15 K)/kJ mol−1 and the standard enthalpies of sublimation ΔHS(298.15 K)/kJ mol−1 are as follows: −4000.36±0.67 and 86.9±1.5 for 1,2-dicyanobenzene; −3992.29±0.75 and 90.1±1.5 for 1,3-dicyanobenzene; −3988.04±0.59 and 88.8±1.5 for 1,4-dicyanobenzene, respectively. Thermochemical destabilization energies were estimated by comparing the derived standard enthalpies of formation in gaseous state with those estimated for hypothetical non-destabilized molecules. They were discussed in terms of electrostatic interactions between highly electronegative and dipolar cyano substituents on one and the same benzene ring. Dipole moments of the dicyanobenzenes in benzene and dioxane solutions are reported in Appendix.