engleski

Chemical bonds and topochemical effects

The thermally induced E-Z isomerization of the benzeneazodioxide derivatives is studied in the solid polychrystalinic state. The reactions are studied from the kinetic and mechanistic aspects. In contrast to the solution, where isomerizations of azodioxides proceed through the formation of corresponding nitroso monomers, in solid state the reaction follows the mechanism that includes formation of the “torsional” transition state, as it is the case in other known cis-trans isomerizations. It is proposed that both the reactions in solid state, the nitroso monomer-dimer equilibrium, and isomerization about the azodioxide N=N bond involve similar transition states. The drift for the transformation of Z- to E-isomer is the phase transformation, since the E-isomer crystal phase of the product is significantly more stable than the Z-crystal phase. Similar concurrent reactions were found in the solid-state polymerizations of 1, 4-dinitrosobenzenes. The reactivity of dimereization and isomerization strongly depends on the topochemical conditions. We demonstrate that the strong topochemical effect can stabilize the structures in the potential energy minima that are shorter than van der Waals bonds and longer than the normal covalent bond.

solid-state; E-Z isomerization; transition state; monomer-dimer; nitroso

nije evidentirano