text: The effect of solvent on elimination and nucleophillic substitution reactions was originally studied by British chemists Edward D. Hughes and Christopher Kelk Ingold. Using a simple solvation model that considered only pure electrostatic interactions between ions or dipolar molecules and solvents in initial and transition states, all nucleophilic and elimination reactions were organized into different charge types (neutral, positively charged, or negatively charged).
  Hughes and Ingold then made certain assumptions about the extent of solvation to be expected in these situations:
  * increasing magnitude of charge will increase solvation
  * increasing delocalization will decrease solvation
  * loss of charge will decrease solvation more than the dispersal of charge 
  The applicable effect of these general assumptions are shown in the following examples:
  * An increase in solvent polarity accelerates the rates of reactions where a charge is developed in the activated complex from neutral or slightly charged reactant
  * An increase in solvent polarity decreases the rates of reactions where there is less charge in the activated complex in comparison to the starting materials
  * A change in solvent polarity will have little or no effect on the rates of reaction when there is little or no difference in charge between the reactants and the activated complex.