Arylacetic special

We may make the assumption that is the sum of inductive and resonance effects (cj, + aR = ap). To a near approximation = a, because with the meta substituent there can be no through resonance. Special a values have been defined (a°, a", a ) where through resonance is absent values are usually derived from side-chain reactions insulated from the aromatic ring by one or two methylene groups. Values of a" are from ordinary a values where a p value is obtained for a reaction using substituents free of resonance interaction. Values of a may then be calculated from the basic Hammett regression line. Values of a were defined from the rates of alkaline hydrolysis of ethyl arylacetates. 

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