Boron-Nitrogen System

II. 4.2), whereas ring systems other than the six-membered borazines are the exception for boron-nitrogen systems. The reasons for this different behaviour will be discussed in later chapters. 

Mass spectral data have frequently been used in the structural determination of boron heterocycles. One paper has been devoted to the mass spectra of some six-membered boron-nitrogen systems. It was concluded that the spectra could be interpreted analogously to their hydrocarbon counterparts. In all cases the molecular peak was the base peak of the spectrum (68T6755). Doubly charged molecular ions, a feature typical of aromatic compounds, are often encountered. It should be noted, however, that some certainly non-aromatic aminoboranes give such doubly charged ions as well. 

The concept of isosterism between the atom groupings B-N and C-C, when introduced more than 60 years ago, implied the expectation that a relatively extensive boron-nitrogen system of compounds, analogue to hydrocarbons, should be forthcoming. 

For the boron-nitrogen system, because the high gas pressure is required for the synthesis, it is difficult to apply any dynamic method for investigation of the microstructural transformations, which occur in the combustion front. Thus, the static quenching technique was used [26, 23, 27]. The idea of this method is to extinguish the combustion wave and quickly cool the sample it is necessary to freeze all zones with the characteristic microstructure, chemical and phase structure of the reactants, intermediates, and final products. For quenching to take place, the heat loss from the reaction front at some point must exceed the critical... 

Figure 2.9 schematically represents mechanism of BN a formation in the combustion wave. For the boron-nitrogen system, the liquid-phase edge in which boron and nitrogen dissolve acts as a chemical pump. Apparently, in case of... 

The borazines and aminoboranes are examples of compound types that are isoelectronic with benzene and ethylene, respectively. Although the preparation, reaction (predominantly substitution and addition reactions), and physical properties of these boron-nitrogen systems have been extensively studied (1,2) little has been done toward investigating their electronic nature with respect to the reactions or subtle interactions that are characteristic of the corresponding carbonoid systems where electron delocalization is known to occur. 

Boron nitride (BN) is the only major compound known in the boron-nitrogen system although a nitrogen rich composition has recently been reported (see Sec. 3.5 below). 

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