Sigma- and pi- electron structure of aza-azoles

Tadeusz M. Krygowski (1) , Wojciech P. Oziminski (2, 3) , Christopher A. Ramsden (4)

1 Faculty of Chemistry [Warsaw]
2 NIL - National Medicines Institute - Narodowy Instytut Leków [Warsaw]
3 INCT - Institute of Nuclear Chemistry and Technology
4 Lennard-Jones Laboratories, School of Physical and Geographical Sciences

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 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 (π) against the relative occupation of σ orbitals (σ) for all individual atoms in rings.

Mots clés: Aromaticity; Azoles; HOMA; NBO; NICS; pEDA; sEDA

Tadeusz M. Krygowski, Wojciech P. Oziminski, Christopher A. Ramsden. Sigma- and pi- electron structure of aza-azoles. Journal of Molecular Modeling, 2010, 17 (6), pp.1427-1433. ⟨10.1007/s00894-010-0844-z⟩. ⟨hal-00624428⟩