ИСТИНА

Dynamic behavior of molecular systems is regularly associated with some sort of chemical reactions. There are still numerous examples of extremely rapid dynamics, which can’t be sufficiently evaluated in terms of classical kinetic parameters. Accurate structure studies of open-chain compounds and saturated four- and five-membered cycles imply solving specific problem of quantitative description of dynamic processes with no or very low barriers [1]. In recent time, quantum molecular dynamics methods [2] based on the large-amplitude vibration model have been widely used to describe various spectral and photochemical properties of organic molecules. Proper consideration of the internal rotation dynamics improves the accuracy and reliability of prediction of spectral parameters, in particular spin–spin coupling constants [3], which could provide key information for solving structural organic chemistry problems. These methods enable quantitative simulation of such fast processes as restricted internal rotation and inversion, which opens new prospects for conformational analysis of various acyclic systems, four-, five- and seven-membered rings, etc [4]. We developed a practical method for evaluation of the parameters of conformational dynamics in terms of vibrations with large amplitude. The method based on: (i) complete analysis of high resolution NMR spectra, (ii) ab’initio calculations of a reaction paths and surfaces of spin-spin coupling constants, (iii) a numerical solution of vibration problem and (iv) refinement for the parameters of the potentials based on the best fit of experimental and calculated spin-spin couplings (see e.g. [4 - 6]). Advantages of the technique demonstrated on studies of pseudorotation in four- and five-membered cycles and internal rotation in acyclic systems: vinylcyclopropane, styrene, cynnamic aldehyde and azobenzene. The dynamic structure of natural endogenic hormones adrenalin and noradrenalin as well as chemical warfare agent soman have been studied with the goal of obtaining accurate structural information to simulate molecular mechanisms of their action in living systems.