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]/32.4DIMROTH, REICHARDT, SIEPMANN and BOHLMANN (1963); REICHARDT (1988). See also Grunwald-Winstein equation, Z-value.
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