Equilibrium and basicity

One of the first indications of the applicability of a linear free-energy treatment to aromatic substitution was the observation of a linear relationship between the equilibrium basicity and halogenation rates of the polymethylbenzenes (Fig. 5). Condon (1948) was able to calculate the rates of halogenation of the polymethylbenzenes with reasonable precision on the basis of a linear free-energy treatment. 

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