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Structural Chemistry

, Volume 18, Issue 6, pp 833–839 | Cite as

Borazine: to be or not to be aromatic

  • Rafael Islas
  • Eduardo Chamorro
  • Juvencio Robles
  • Thomas Heine
  • Juan C. Santos
  • Gabriel Merino
Original Paper

Abstract

Aromaticity of borazine, which has been subject of controversial discussions, is addressed. Beside a short review on aromaticity of borazine we report a detailed analysis of two molecular fields, the induced magnetic field (B ind) and the electron localization function (ELF). The induced magnetic field of borazine shows a long-range shielding cone perpendicular to the molecular plane, as in benzene, but lower in magnitude. Contrary to benzene, borazine shows two weakly paratropic regions, one of them inside the ring, and the second one enveloping the boron atoms. It is necessary to separate σ and π contributions to identify whether borazine exhibits π-aromatic character comparable to benzene. Nucleus-independent chemical shift (NICS) isolines show that the σ electrons are much stronger localized than π electrons, their local paramagnetic contributions generate a short-range response and a paratropic (deshielding) region in the ring center (similar to an anti-aromatic response). Three regions can be identified as chemically meaningful domains exhibiting an internally strong electron delocalization (ELF = 0.823). Borazine may be described as a π aromatic compound, but it is not a globally aromatic species, as the electronic system is not as delocalized as in benzene.

Keywords

Aromaticity Borazine ELF NICS Induced Magnetic Field 

Notes

Acknowledgments

This work was funded in part by grants from DINPO-UGTO, and the Deutsche Forschungsgemeinschaft (DFG). RI gratefully acknowledges a Conacyt Ph.D. fellowship. JCS and EC thank Fondecyt (Chile), grants 11060197 and 1070378, and the Millennium Nucleus for Applied Quantum Mechanics and Computational Chemistry (Mideplan-Conicyt, Chile), grant P02-004-F for continuous support. JCS and EC also thank to UNAB by support through the DI 22-05/R and 21-06/R research grants.

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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  • Rafael Islas
    • 1
  • Eduardo Chamorro
    • 2
  • Juvencio Robles
    • 1
  • Thomas Heine
    • 3
  • Juan C. Santos
    • 2
  • Gabriel Merino
    • 1
  1. 1.Facultad de QuímicaUniversidad de GuanajuatoGuanajuatoMexico
  2. 2.Departamento de Ciencias Químicas, Facultad de Ecología y Recursos NaturalesUniversidad Andres BelloSantiagoChile
  3. 3.Institut für Physikalische Chemie und ElektrochemieTU DresdenDresdenGermany

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