The definition and theoretical fundamentals of a new scientific trend—chemical mesoscopics—are considered in the example of a new class of nanostructures: metal/carbon nanocomposites (NCs). The theoretical and experimental methods for the processes direction prognosis as well as for the chemical systems reactivity estimation are discussed. The hypothesis of mesoscopic metal-containing cluster creation at mechanic–chemical formation of metal/carbon NCs is proposed. The electron structures of carbon shells for metal-containing clusters are determined. The metal nature influence of metallic phase cluster on the carbon shell is shown. The media electron structure changes are possible under the influence of even minute quantities of NCs, and it is confirmed by the X-ray photoelectron spectroscopic investigations and also is explained by the Chemical Mesoscopics principles. It is shown that the orientation processes, in which mesoscopic particles (NCs) participate, lead to the changes of sub-molecular structures of polymeric compositions.