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Organic Polarography, Structure and Linear Free Energy Relationships

1963; Volume: 11; Issue: 1-2 Linguagem: Inglês

10.5189/revpolarography.11.102

1884-7692

P. Zuman,

Photochemistry and Electron Transfer Studies

It was like in an old fairy tale: When Professors J. Heyrovský and M. Shikata parted, each brought a problem with him home : There were mainly inorganic problems studied in Czechoslovakia whereas much stress has been laid on organic polarography in Japan. This division even when not without notable exceptions remained until early forties. It is thus not surprising that it was from the pen of M. Shikata and I. Tachi from which the first papers on correlations between the structure and polarography of organic substances appeared. The famous Shikata-Tachi rule was a guide of organic polarographers for almost two decades, basing on the qualitative knowledge of theoretical organic chemistry of these days.Since then organic polarography broadened considerably its scope and also the understanding of the electrode processes got more profound. Japanese scientists joint in this venture and helped to our understanding of the polarographic behaviour of organic substances. Professor I. Tachi and his coworkers contributed substantially in this respect. When the quantitative treatment of structural effects was developed, polarography applied such methods to the treatment of half-wave potentials. Again Japanese chemists took part in that development (cff the references later in the text part). Thus it is a great priviledge to contribute to the volume devoted to Professor I. Tachi in the field he himself fostered. In addition to rate and equilibrium constants, for which these relationships were originally devised, several physico-chemical quantities were correlated using Hammett and Taft equation and similar free energy relationships. Whereas for most other physico-chemical quantities, like the wave-length of the maximum of a selected band in UV-spectra or like quadrupole coupling constants, these correlations are at present purely empirical, for polarographic half-wave potentials the explanation for such correlations between electrochemical data and equilibrium and kinetic data (expressed through the values of the substituent c constants) can be suggested.