Three types of organic solid‐state reactions, dimerizations, dissociations, and Z‐E isomerizations were investigated by using the transformations of aromatic C‐nitroso compounds in crystalline solids as a convenient molecular model. Here we propose a conceptual frame for solid‐state organic reaction mechanisms by examining activation parameters obtained from kinetic measurements under specific experimental conditions. The possibility of the appearance of a sort of short‐lived intermediate liquid phase that constitutes a critical condition for initiating chemical reaction in crystalline solids, similarly to the mechanism for the thermal solid‐state reactions proposed by Paul and Curtin is discussed. The analogy of the proposed concept with the recent hypothesis about the variable rigidity/softness of the reaction cavity in the enzyme reactions, and with the newest molecular dynamic simulation studies of solid phase transformations was considered. The role of the rigidity/softness of the reaction cavity in the mechanisms of organic solid‐state reactions was investigated by measuring activation parameters of interconversions of aromatic nitroso/azodioxides structures in crystalline solids. The results obtained suggest possible analogies between the reaction mechanisms in crystalline solids and in other condensed media.