A theoretical treatment of Hammett's sigma constants
- 1 January 1953
- journal article
- research article
- Published by Wiley in Recueil des Travaux Chimiques des Pays-Bas
- Vol. 72 (8) , 673-690
- https://doi.org/10.1002/recl.19530720807
Abstract
A theoretical treatment is given of the connection between the structure and the position of a substituent S and the value of σs, from the Hammett equation: log ks/ko = ρ · σs. The theory is based on a wave mechanical calculation of the effect of S on the localisation energy of a reaction. The equations derived make it possible to calculate σs, for a large number of substituents from known values of bond lengths and bond moments.The calculations are carried out for a number of different reaction types, which are representative of a large number of reactions. The mean deviation of the theoretical values of σ from the experimental values amounts to ±0.07; the agreement reached is of the same order, therefore, as the experimentally found deviations from Hammett's equation.Keywords
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