2. Specific Intermolecular Interactions of Cyclic Alkylamines and Nitriles

Among modern ideas, controversies on the n-orbital of the ammonia molecule are reflected on the photoelectron spectra of amino-derivative compounds [1–3]. Violation of the nuclear framework of the molecules of noncyclic alkyl compounds in the range of the trigonal pyramid to plane ones with removal of the n-electron leads to a wide oscillatory circuit of the first FE-bands, which appears at the intramolecular and intermolecular interactions. As a result a change in the coordinating ability of the nitrogen atom takes place and the specific interactions gain thermal stability . Despite the great number of papers on photoelectron spectra the best conformity with inclusion of the vertical ionization potential Iv has been established for the mono-substituted methylamine. It means that the maximum value in thermodynamic construction and specificity of the intermolecular interaction should be reflected precisely in this connection. It was shown above that all linked vacancies of the molecules close to the environment in liquid ammonia are realized in a coordinated state with six nitrogen atoms with the location of the hydrogen atoms on top of the trigonal pyramid (Fig. 2.1), forming a similar structure at the interaction of the nitrogen atom of the ammonia molecule in contact. Hydrogen atoms or alkyl groups of the pyramid base of the interacting molecules are located at maximum distance, which is never reached because their locations relative to each other are not symmetrical. Regarding the productivity of this approach we note that for reliable determination of changes of Н-cohesion of a molecule in condensed condition one should indicate changes in coordination when changing the structure of ammonia and all amino-derivative compounds on planar structure with the nitrogen atom, acting as coordinating center in, for example, hydrazones . The equivalence of all six hydrogen bonds of one type and its gap in the transition of the ammonia molecule to steam allows the use of enthalpy characteristics of the corresponding process to determine the energy of the hydrogen bonds in the condensed state. It follows that the energy of the Н-bond N–H•••N is equal to the quotient of the sublimation enthalpy and evaporation of the number of realized hydrogen bonds [4–6]. The results of the calculation performed show reduced stability of the hydrogen bond, formed by the nitrogen atom of the ammonia molecule with the structure of a trigonal pyramid (4.23 and 3.86 kJ mol⁻¹), being less stable compared with coordination of the four hydrogen atoms (6.34 and 5.91 kJ mol⁻¹) with planar structure of the molecule in solid and liquid states, respectively.