Experimental thermochemical study of the monochloronitrobenzene isomers

The standard (p∘ = 0.1 MPa) molar enthalpies of formation of 2-, 3-, and 4-chloronitrobenzene isomers, in the crystalline state, at T = 298.15 K, were derived from the standard (p∘ = 0.1 MPa) massic energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of sublimation of the isomers, at T = 298.15 K, were obtained by high temperature Calvet microcalorimetry.-ΔcUm∘(cr)/(kJ · mol−1)-ΔcHm∘(cr)/(kJ · mol−1)-ΔcrgHm∘/(kJ · mol−1)2-Chloronitrobenzene2939.5 ± 0.718.7 ± 1.080.9 ± 1.53-Chloronitrobenzene2915.8 ± 0.842.4 ± 1.282.5 ± 1.54-Chloronitrobenzene2921.7 ± 1.436.5 ± 1.676.2 ± 2.1Full-size tableTable optionsView in workspaceDownload as CSVFrom the determined experimental data, the values of the gaseous standard (p∘ = 0.1 MPa) molar enthalpies of formation for the three monochloronitrobenzene isomers were derived. The gas-phase enthalpies of formation were also estimated by the empirical scheme developed by Cox showing that for meta- and para-chloronitrobenzene the estimated values are in close agreement with the experimental ones whereas, in the case of ortho-chloronitrobenzene it is shown that a different enthalpic interaction increment is needed, when the substituents in the adjacent carbon ring atoms are a chlorine atom and a nitro group.