Definition of Dimroth-Reichardt ET parameter

1. A measure of the ionizing power (loosely polarity) of a solvent, based on the maximum wavenumber of the longest wavelength electronic absorption band of

   

   in a given solvent. ET, called ET(30) by its originators, is given by

   ET = 2.859 x l0-3= 2.859 x 104-1where ET is in kcal/mol, is in cm-1 and is in nm.

   The so-called normalized ETN scale is defined as

   ETN = [ET(solvent) - ET(SiMe4)]/[ET(water) - ET(SiMe4)] = [ET(solvent) - 30.7]/32.4

   DIMROTH, REICHARDT, SIEPMANN and BOHLMANN (1963); REICHARDT (1988). See also Grunwald-Winstein equation, Z-value.