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Aromaticity and conformational flexibility of six-membered rings: influence of heteroatoms and substituents


Author:Omelchenko I. V.

Presented by the SSI STC “Institute for Single Crystals” NAS of Ukraine.

A series of work consists of 6 papers and 8 conference thesis published in 2006 – 2013.

The work is devoted to study of the effect of heteroatoms and substituents in aromatic rings on the aromaticity and conformational flexibility of the six-membered rings.

Series of fundamental results were obtained. The dependence of changes of aromaticity and ring flexibility with respect to the type of heteroatom was systematized for monoheterocyclic analogues of benzene. Special features of cyclic conjugated system in pyrylium cation and in heterocycles with heteroatoms of III-IV period were revealed. The difference between donor and acceptor substituents was found studying effect of the substituent on aromaticity of monosubstituted benzenes. A quantitative dependence was established between the substituent constants and energies of deformation of corresponding aromatic rings. For polysubstituted benzenes with nitro- and amino groups, the forming of intramolecular resonance-assisted hydrogen bonds was determined as a key factor of the changes in the cyclic π-conjugation. At the time it was shown that, in nitro- and amino substituted monoheterocycles, the push-pull effect is the main factor of aromaticity changes. Unusually high conformational flexibility and low degree of aromaticity was revealed studying aromatic rings at the room temperature, as compare to their behavior at 0 K. It was shown that the entropy factor plays a critical role in such cases, and its influence on high symmetrical benzene molecule is much more than on low symmetrical molecules of heterocycles.

New approach to the theoretical analysis of conformational characteristics of aromatic rings at the nonzero temperature and including entropy factor was introduced. The energy of deformation of the ring was shown as a new structural-dynamic aromaticity index.

A basis for prognostic models was created that predict change of different physico-chemical parameters as a function of their element composition and structural surrounding. New approaches with using of molecular dynamic methods allow predicting conformational characteristics of the cycles at nonzero temperature and related spectral features. Quantitative parameters obtained during the research can be used for adjustment of force fields for classical molecular dynamics that are widely used for modeling of complex biological systems. Also, the work is important for high school teaching purposes because it strongly perturbs classical view on the aromaticity, as well as its role in energetic stabilization, heteroatom and substituent influence, and flexibility of aromatic rings.

Results are presented in 14 publications, including 6 papers in referred scientific journals and 8 conference theses. These works were cited 69 times according to Scopus, the publication h-index is 4. Overall number of citations of all authors’ papers is 130, her h-index is 6. Those works were cited in more than 30 scientific journals.