Addition compounds dinitrobenzene isomers

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... 

Exposure. Exposure to 1,3-DNB is currently measured indirectly by determining levels of methemoglobin in the blood (Donovan 1990). However, increased methemoglobin formation is not a specific response to 1,3-DNB exposure and may occur after exposure to other nitrobenzene compounds such as the other two isomers of dinitrobenzene. Determination of methemoglobin levels is widely used and is a reliable detection method. Very few methods are available for direct evaluation of 1,3-DNB levels, and they are not extensively used, probably because of the relatively rapid rate of conversion of 1,3-DNB to its degradation products (Cossum and Rickert 1985). Preliminary data suggested that the formation of adducts of 1,3,5-TNB with tissue DNA and/or with blood proteins may be useful as markers for exposure to 1,3,5-TNB (Reddy et al. 1991). Further research with both 1,3-DNB and 1,3,5-TNB in the area of adduct formation could provide valuable additional information. 

There are enthalpy of formation data for the 2,4- and 4,6-dinitro-l,3-benzenediols. From the archival enthalpy of formation of solid m-dinitrobenzene and 5 (OH/H), the enthalpy of formation of either dinitrobenzenediol isomer is predicted to be —434.2 kJ moH. Compared to this estimated value, the 2,4-isomer is ca 11 kJ moH destabilized and the 4,6-isomer is ca 9 kJ mol stabilized. Each of these compounds has a pair of meta hydroxy groups, a pair of meta nitro groups and two pairs of ortho hydroxy/nitro groups. The 2,4-isomer has an additional ortho hydroxy/nitro interaction. 

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