Term: Dimroth–Reichardt ET parameter
https://doi.org/10.1351/goldbook.D01746

Definition:
A measure of the ionizing power (loosely polarity) of a solvent, based on the maximum wavenumber of the longest wavelength electronic absorption band of: D01746.png in a given solvent. ET, called ET(30) by its originators, is given by: \[E_{\text{T}} = 2.859\times 10^{-3}\ \nu = 2.859\times 10^{4}\ \lambda ^{-1}\] where ET is in kcal mol-1, ν is in cm-1 and λ is in nm. The so-called normalized ETN scale is defined as: \[E_{\text{T}}^{\text{N}}=\frac{E_{\text{T}}\left(\text{solvent}\right)- E_{\text{T}}\left(\text{Si}\text{Me}_{4}\right)}{E_{\text{T}}\left(\text{water}\right)- E_{\text{T}}\left(\text{Si}\text{Me}_{4}\right)}=\frac{E_{\text{T}}\left(\text{solvent}\right)- 30.7}{32.4}\]

Related Terms:
1) grunwald–winstein equation (http://doi.org/10.1351/goldbook.G02710).
2) <em>z-value</em> (http://doi.org/10.1351/goldbook.Z06737).
3) ionizing power (http://doi.org/10.1351/goldbook.I03215).
4) polarity (http://doi.org/10.1351/goldbook.P04710).
5) wavelength (http://doi.org/10.1351/goldbook.W06659).

Image: Not defined (https://goldbook.iupac.org/img/inline/D01746.png) 

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1106 (https://doi.org/10.1351/pac199466051077)

Citation: 'Dimroth–Reichardt <em>E</em><sub>T</sub> parameter' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.D01746

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