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Sigma- and pi- electron structure of aza-azoles |
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| Authors: | Tadeusz M Krygowski Wojciech P Oziminski Christopher A Ramsden |
| Institution: | (1) Department of Chemistry, University of Warsaw, Pasteura 1, 02 093 Warsaw, Poland;(2) National Medicines Institute, Chełmska 30/34, 00 725 Warsaw, Poland;(3) Institute of Nuclear Chemistry and Technology, Dorodna 16, 03 195 Warsaw, Poland;(4) Lennard-Jones Laboratories, School of Physical and Geographical Sciences, Keele University, Keele, Staffordshire, ST5 5BG, UK; |
| Abstract: | The reasons behind changes of aromaticity in 10 unsubstituted aza-azoles were analysed by employing the natural bond orbital (NBO) approach at the MP2/6-311+G(d,p) level of theory. Sum of occupations of p z orbitals at atoms in the ring correlates well with the magnetism based aromaticity index NICS as well as with the number of nitrogen atoms in the ring. Changes of NICS depend strongly in a linear way on the number of NN bonds. Classification of azoles based on the number of pyridine-type nitrogen atoms vicinal to NH is supported by plotting the relative occupation of π orbitals (πocc) against the relative occupation of σ orbitals (σocc) for all individual atoms in rings. |
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