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

One of the most exploited approaches in scientific methodology is studying concepts by using a case study. In chemistry, a case study appears in finding a specific molecular and/or reaction system by which the investigated problem can be observed directly "on substance". Thus, the stu- died problem becomes a concrete system, rather than an abstract concept. Most case-study models are designed specifically to deepen one or another chemical problem. However, there exist (although rarely) models, which afford their universality, i.e. could serve for modeling of qui- te different, and even epistemologically independent concepts. Systematic investigations of the chemistry of C-nitroso compounds performed in our Laboratory in last few years, have resulted in the discovery that such molecular system may be used as a model for studying a series of basic chemical concepts; selectivity, self-assembly, solid-state reaction mechanisms, photochromism and molecular logics. Since it is known that C-nitroso compounds under specific conditions dime- rize by forming new N=N bond (Scheme 1), the reaction can be used for studying selectivity in the formation of dimers between different nitroso monomers (Fig. 1 and Fig. 2). The system is very convenient 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 di- mers. These discoveries inspired us to investigate the kinetics and mechanism of dimerization of nitroso monomers in solid state, because the freshly sublimed nitrosoaromatic compounds appear as crystals of monomers. Consequently, this molecular system is a perfect case-study model for concepts of solid-state reactions, self-organizations in the crystalline forms (Fig. 3), as well as for the8,13 Extending our research of self-organization of nitroso compounds to two-dimensional systems (Fig. 4), we have also de- monstrated the 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 crystallized dimers observed by the change in color, also demonstrated that this molecular system could be one of the basic models for molecular logic gates (Fig. 7). 16From the presented examples it follows that this molecular model of dimerizations of aromatic nitroso compounds affords its epistemic universality.