1.4- Dinitro-benzene calculation

Some heats of sublimation of organic compounds calculated from the Clapeyron-Clausius formula ( 7.VIIIL) were in disagreement with Trouton s rule as calculated ( 14.VIIIL) for 4=4—4 and are of doubtful accuracy. They increased in the order ortho-, meta-, and para- compounds for dinitro-benzenes and nitroanilines, but the theoretical deductions made would be more interesting if greater confidence could be attached to the experimental results. The calculation of latent heats of sublimation from lattice theory is mentioned in 15.IXN. 

A polarity parameter is also calculated with the ratio of polarity and the distance between the atoms that possess the maximum and minimum charge. In this case, the para-dinitro-benzene appears as a very polar molecule because the distance between the atoms of nitrogen and oxygen is small. 

Table 3 presents the experimental enthalpies of formation of polynitrobenzenes and Table 4 presents the calculated additivity values and DSEs for these same compounds. Enthalpy-of-formation values have been determined experimentally for all three dinitrobenzene isomers in the gaseous state. The enthalpy-of-formation difference between the meta and para isomers is indistinguishable from 0. Conventional wisdom suggests that the para isomer should be destabilized relative to the meta because of adjacent positive charges in key ionic or polar resonance structures. Thus it seems that electronic effects due to meta/para dinitro substituent position are small. This small enthalpy-of-formation difference is similar to that for the meta and para dicyano, difluoro and dichloro benzenes, but does not mimic the ca 22 kJ mol 1 difference for the phthalic acids with which the... 

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