The impact reactivity ("the first reaction") of 22 polynitro arenes was expressed as the drop energy, E-dr, required for 50 percent initiation probability. Relationships have been found between the E-dr values and heats of fusion, on the one hand, and C-13 NMR chemical shifts of carbon atoms in reaction centers, on the other hand. On the basis of the said relationships it was stated that the impact reactivity of polynitro arene molecules depends on the electronic configuration within their reaction centers and on the intensity of their intermolecular interactions in the molecular crystals. The relationships found make it possible to specify this reaction center which is illustrated by the molecules of 1,5-dinitronaphthalene and 3,3'-dimethyl-2,2',4,4',6,6'-hexanitrodiphenyl sulfide.