Dimroth–Reichardt E T parameter

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. E T, called E T 30 by its originators, is given by:
E T = 2.859 × 10 −3 ν = 2.859 × 10 4 λ −1
where E T is in kcal mol −1, ν is in cm −1 and λ is in nm. The so-called normalized E T N scale is defined as:
E T N = E T solvent − E T Si Me 4 E T water − E T Si Me 4 = E T solvent − 30.7 32.4
See also: Grunwald–Winstein equation, Z-value
PAC, 1994, 66, 1077 (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1106