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A Raman approach to pseudo-cross-conjugation in mesomeric betaines

  1. C. Capel Ferrón1,
  2. J. Casado1,
  3. J. T. López Navarrete1,
  4. A. Dreger2,
  5. A. Schmidt2,
  6. F. J. Ramírez1,*

Article first published online: 11 FEB 2009

DOI: 10.1002/jrs.2208

Issue

Journal of Raman Spectroscopy

Journal of Raman Spectroscopy

Volume 40, Issue 3, pages 238–239, March 2009

Additional Information

How to Cite

Capel Ferrón, C., Casado, J., López Navarrete, J. T., Dreger, A., Schmidt, A. and Ramírez, F. J. (2009), A Raman approach to pseudo-cross-conjugation in mesomeric betaines. J. Raman Spectrosc., 40: 238–239. doi: 10.1002/jrs.2208

Author Information

  1. 1

    Departamento de Química Física, Facultad de Ciencias, Universidad de Málaga, Málaga 29071, Spain

  2. 2

    Institute of Organic Chemistry, Clausthal University of Technology, Leibnizstrasse 6, D-38678 Clausthal-Zellerfeld, Germany

*Departamento de Química Física, Facultad de Ciencias, Universidad de Málaga, Málaga 29071, Spain.

Publication History

  1. Issue published online: 6 MAR 2009
  2. Article first published online: 11 FEB 2009
  3. Manuscript Accepted: 18 DEC 2008
  4. Manuscript Received: 24 OCT 2008

Funded by

  • Spanish Ministry of Science and Technology. Grant Number: CTQ2006-14987-C02-01

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Keywords:

  • phenylpyrazolium;
  • mesomeric betaine;
  • Raman spectra;
  • pseudo-cross-conjugation

Abstract

We demonstrate that Raman spectroscopy is able to discriminate between cross-conjugated (CC) and pseudo-cross-conjugated mesomeric betaines (PCCMBs) by means of key bands sensitive to conjugation. As targets, we have selected the PCCMB 2,5 dimethyl-1-phenylpyrazolium-3-carboxylate and its isomer the CCMB 1,3-dimethyl-2-phenylpyrazolium-4 carboxylate. Structurally, they differ only in the position of the carboxylate group bonded to the pyrazolium ring. However, this feature provides different conjugational character. We provide evidences for the fact that this structural difference has a measurable impact in the vibrational wavenumbers as Raman spectroscopy can directly account for it. We also prove that the observed Raman features are not only originated by the kinetic effect caused by the change of the carboxylate position, but this atomic re-organization also modifies the potential energy of the molecule. This energy directly depends on the electronic structure, which determines the pseudo-cross-conjugation character. Copyright © 2009 John Wiley & Sons, Ltd.

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