The rate coefficients for the esterification with diazodiphenylmethane in ethanol at 30° and the pK a values at 25° of a number of ortho-substituted trans-cinnamic, phenoxyacetic, 3-phenylpropionic, ortho-, meta-, and para-substituted cis-trans-α-phenylcinnamic acids have been determined. The effects of substitution have been assessed by a Hammett-type correlation. A comparison of the transmission of the polar effects of ortho and meta/para substituents indicates the prime importance of the field effect, augmented where possible by a π-inductive effect. A reversed dipolar substituent field effect has been detected for the cis-ortho-substituted cinnamic acids.
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Bowden et al. (1968) studied this question.