ИСТИНА

Dynamic behavior of molecular systems is normally associated with some sort of chemical reactions. There are still numerous examples of extremely rapid dynamics, which can’t be described in terms of classical kinetic parameters, such as reaction rates, activation parameters etc. It even is better to consider them in terms of vibrations with large amplitude. Accurate structure studies of saturated four- and five-membered cycles imply solving specific problem of quantitative description of dynamic processes with very low barriers in them. Examples of accurate microwave studies are known of only few simplest such systems in gaze phase. Advantages of the technique developed demonstrated on a series of monosubstituted cyclobutanes, trans-1,2-dihalocyclopentanes, tetrahydrofuran, tetrahydrothiophene, tetrahydrothiophene-1-oxide, pyrrolidine, proline and ribonucleosides. The data obtained shows, that the pseudorotation process in every four- and five-membered system under study is carrying out by the mechanism with high amplitude of vibration. Major conformations of tetrahydrofuran and terahydrothiophene are twists 4Т5 and 5Т4, for pyrrolidine – envelope Е1 with equatorial NH-bond, for terahydrothiophene-1-oxyde – envelopes Е3 and with axial oxygen and for proline – envelope Е5 with axial СООН-group. Method used also for characterization of internal rotation in acyclic systems – natural endogenic hormone adrenaline and substituted azobenzenes.