Dewar-Grisdale equation

The second approach is more rigorous here the p-values are taken as equivalent to that in benzenoid compounds and cr-values are calculated for the thiophene substituents. The calculation may take into account the differing geometries of the two ring systems (use of the Dewar-Grisdale equation). 

The Dewar-Grisdale Equation An approach to field and resonance transmission of the polar effect essentially the same as that of Taft s group was suggested by Dewar and Grisdale. The localised and delocalised polar effects are represented by F and M which are taken to be additive in any given a value. The value a,y is related to the sum of... 

The Swain-Lupton, Taft and Dewar-Grisdale equations all require that the substituent in the reaction under investigation remains at the same position relative to the reaction centre. Thus meta and para series have to be treated separately unlike the Yukawa-Tsuno method where both meta and para substituents may be taken together. The Swain-Lupton treatment may be illustrated by the reaction of chloride ion with substituted benzenediazonium chlorides (Figure 7, Equation 26). ... 

The Dewar-Golden-Harris approach (DGH), also called FMMF method (i.e. Field, Mesomeric and Mesomeric-Field method) [Dewar et al, 1971a] is a modification of the Dewar-Grisdale approach, where the substituent X is approximated by a finite dipole (represented by two point charges along the /-X bond) and the reaction site at position i as a single point charge. This approach is based on the equation ... 

The Yukawa-Tsuno and Young-Jencks equations have the advantage that they utilise both meta and para substituents in the same equation unlike the Dewar-Grisdale and Swain-Lupton equations (Sections... 

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