The π-Electron Delocalization Imposed by Thermal Vibrations of Substituted Benzene Analogues in Mediums of Varying Polarities
Cysewski Piotr 1,2, Jeliński Tomasz 1
1 Department of Physical Chemistry, Collegium Medicum, Nicolaus Copernicus University ul.Kurpińskiego 5, 85-950 Bydgoszcz, Poland
e-mail: piotr.cysewski@cm.umk.pl
2 Department of General Chemistry, University of Technology and Life Sciences in Bydgoszcz
ul. Seminaryjna 3, 85-326 Bydgoszcz, Poland
Received:
Received: 30 August 2011; revised: 22 November 2011; accepted: 25 November 2011; published online: 20 December 2011
DOI: 10.12921/cmst.2011.17.01.05-16
OAI: oai:lib.psnc.pl:734
Abstract:
The unique set of aromaticity indices was identified for thermally induced changes of π-electron delocalization by means of PCA (Principal Component Analysis). It was demonstrated that solvents polarity can influence not only the values of aromaticity indices but also their contribution to Principal Components. Therefore, in different phases one should select different indices for a proper description of the aromaticity. The found aromaticity diversities indices were provided for aniline as well as p-nitrosoaniline and it was found that the geometry of the latter one is highly sensitive to solvents polarity changes. Thus, all of the aromaticity indices experienced a reduction of their values, with the HOMA (Harmonic Oscillator Model of Aromaticity) index being the most sensitive. It was also found that there were such vibrations which could alter this trend and lead to apparent increase of aromaticity.
Key words:
aromaticity, benzene analogues, normal coordinate analysis, principal component analysis, thermal vibrations
References:
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The unique set of aromaticity indices was identified for thermally induced changes of π-electron delocalization by means of PCA (Principal Component Analysis). It was demonstrated that solvents polarity can influence not only the values of aromaticity indices but also their contribution to Principal Components. Therefore, in different phases one should select different indices for a proper description of the aromaticity. The found aromaticity diversities indices were provided for aniline as well as p-nitrosoaniline and it was found that the geometry of the latter one is highly sensitive to solvents polarity changes. Thus, all of the aromaticity indices experienced a reduction of their values, with the HOMA (Harmonic Oscillator Model of Aromaticity) index being the most sensitive. It was also found that there were such vibrations which could alter this trend and lead to apparent increase of aromaticity.
Key words:
aromaticity, benzene analogues, normal coordinate analysis, principal component analysis, thermal vibrations
References:
[1] E.D. Bergmann, B. Pullman Eds. 1970 Aromaticity, Pseudoaromaticity, Antiaromaticity. Proceedings of an International Symposium, Israel Academy of Sciences and Humanities: Jerusalem, 1971.
[2] P.J. Garrat, Aromaticity. Willey, New York, 1986.
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[7] Z. Chen, C.S. Wannere, C. Corminboeuf, R. Puchta, P.v.R. Schleyer, Nucleus-Independent Chemical Shifts (NICS) as an Aromaticity Criterion. Chem. Rev. 105, 3842-3888 (2005).
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[9] M.K. Cyrański, Energetic aspects of cyclic pi-electron delocalization: evaluation of the methods of estimating aromatic stabilization energies. Chem. Rev. 105, 3773-3811 (2005).
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[19] J. Poater, I. Garcıa-Cruz, F. Illas, M. Solá, Discrepancy between common local aromaticity measures in a series of carbazole derivatives. Phys. Chem. Chem. Phys. 6, 314-318 (2004).
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π-Electron Delocalization of the Pyrene System? J. Org. Chem. 68, 2089-2098 (2003).
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[34] F. Feixas, E. Matito, J. Poater, M. Sola, Aromaticity of Distorted Benzene Rings: Exploring the Validity of Different Indicators of Aromaticity. J. Phys. Chem. A 111, 4513- 4521 (2007).
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[38] A. Julg, P. François, Recherches sur la géométrie de quelques hydrocarbures non-alternants: son influence sur les énergies de transition, une nouvelle définition de l’aromaticité. Theor. Chim. Acta, 7, 249-259 (1967).
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