Aromaticity and conformational flexibility of five-membered monoheterocycles: pyrrole-like and thiophene-like structures |
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Authors: | Irina V. Omelchenko Oleg V. Shishkin Leonid Gorb Jerzy Leszczynski |
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Affiliation: | 1.SSI ‘Institute for Single Crystals’,National Academy of Sciences of Ukraine,Kharkiv,Ukraine;2.V.N.Karazin Kharkiv National University,Kharkiv,Ukraine;3.Badger Technical Services, LLC,Vicksburg,USA;4.US Army ERDC,Vicksburg,USA;5.Department of Chemistry and Biochemistry, Interdisciplinary Center for Nanotoxicity,Jackson State University,Jackson,USA |
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Abstract: | Aromaticity and conformational flexibility of the series of five-membered monoheterocycles with group 14–16 heteroatoms, having one or two lone pairs, were studied with ab initio methods using NICS, ASE and I 5 indices. For non-planar molecules like phosphole, aromaticity of their planar transition states was also studied, and a special modification of ASE index was proposed to that end. It was found that the presence of two lone pairs is generally preferable for aromaticity of all heterocycles except CPD and silolyl dianions. Heterocycles with group 16 heteroatoms have consistently lower aromaticity compared to other groups. A lot of structures should be classified as moderate aromatic and non-aromatic. Energies of out-of-plane deformation do not correlate with other indices studied, but reveal the same qualitative trends. Generally, aromaticity of five-membered monoheterocycles depends strongly on both heteroatom type and number of lone pairs on it. |
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