In Search for Universal Models. Dimerization of Nitrosobenzenes and Investigation of Some Basic Chemical Concepts

摘要

One of the most exploited approaches in scientific methodology is studying concepts by using acase study. In chemistry, a case study appears in finding a specific molecular and/or reaction systemby which the investigated problem can be observed directly “on substance”. Thus, the studiedproblem becomes a concrete system, rather than an abstract concept. Most case-studymodels are designed specifically to deepen one or another chemical problem. However, thereexist (although rarely) models, which afford their universality, i.e. could serve for modeling of quitedifferent, and even epistemologically independent concepts. Systematic investigations of thechemistry of C-nitroso compounds performed in our Laboratory in last few years, have resulted inthe discovery that such molecular system may be used as a model for studying a series of basicchemical concepts; selectivity, self-assembly, solid-state reaction mechanisms, photochromismand molecular logics. Since it is known that C-nitroso compounds under specific conditions dimerizeby forming new N=N bond (Scheme 1), the reaction can be used for studying selectivity inthe formation of dimers between different nitroso monomers (Fig. 1 and Fig. 2). The system is veryconvenient for investigation of the structure-selectivity relations.6 It has already been established,especially in the work of Brian Gowenlock, that nitroso compounds in crystal form appear as dimers.These discoveries inspired us to investigate the kinetics and mechanism of dimerization ofnitroso monomers in solid state, because the freshly sublimed nitrosoaromatic compounds appearas crystals of monomers. Consequently, this molecular system is a perfect case-study modelfor concepts of solid-state reactions, self-organizations in the crystalline forms (Fig. 3), as well asfor the interrelation of phase transition and chemical reaction (Fig. 6).8,13 Extending our researchof self-organization of nitroso compounds to two-dimensional systems (Fig. 4), we have also demonstratedthe ability of such molecules to be models for formation of self-assembly bilayers (Fig.5), and for direct observations of 2D crystallizations.12 The discovery of photodissociation of crystallizeddimers observed by the change in color, also demonstrated that this molecular systemcould be one of the basic models for molecular logic gates (Fig. 7).16 From the presented examplesit follows that this molecular model of dimerizations of aromatic nitroso compounds affords itsepistemic universality.