Department of Chemistry, Osmania University, Hyderabad-7 A.P. Manuscript received 10 March 1975; revised 26 August 1975; accepted 28 August 1975 The rates of base-catalysed condensation of a series of sixteen substituted benzaldehydes with acetone and ethyl methyl ketone were measured colorimetrically. The reaction follows a bimolecular rate law. The plot of log k/k0 vs σ0 for the meta substituted compounds was linear and the ρ values at different temperatures were evaluated. The effective

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... values (σ) for various para substituents and calculation of individual inductive (I) and resonance effects (R) of different substituents have been attempted with the help of Taft equation.