Experimental and computational thermochemical study of the tri-, tetra-, and pentachloronitrobenzene isomers

Abstract

The standard ( p ∘ = 0.1 MPa ) molar enthalpies of formation of 2,4,6-trichloronitrobenzene, 2,3,5,6-tetrachloronitrobenzene, and pentachloronitrobenzene, in the crystalline state, at T = 298.15 K, were derived from the standard massic energies of combustion, in oxygen, at T = 298.15 K, measured by rotating-bomb combustion calorimetry. The standard molar enthalpies of sublimation, at T = 298.15 K, of 2,4,6-trichloronitrobenzene and pentachloronitrobenzene, were determined from the dependence with the temperature of the vapour pressures, measured by the Knudsen mass-loss effusion method, whereas for 2,3,5,6-tetrachloronitrobenzene, the Calvet drop microcalorimetric technique was used. - Δ c U m ∘ ( cr ) /(kJ · mol −1) - Δ f H m ∘ ( cr ) /(kJ · mol −1) Δ cr g H m ∘ /(kJ · mol −1) 2,4,6-Trichloronitrobenzene 2663.5 ± 1.1 58.6 ± 1.3 86.7 ± 1.1 2,3,5,6-Tetrachloronitrobenzene 2537.1 ± 1.7 67.0 ± 1.9 91.3 ± 2.5 Pentachloronitrobenzene 2387.4 ± 2.4 98.6 ± 2.5 94.5 ± 0.4 The experimental values are also compared with estimates based on G3(MP2)//B3LYP computations, which have also been extended to all the isomers of the trichloro- and tetrachloronitrobenzene that were not studied experimentally.