Rate coefficients have been determined for the reactions in ethanol at 30° of diazodiphenylmethane with several groups of carboxylic acids. Each group included the parent acid and three nuclear substituted acids. The parent acids were: benzoic, phenylacetic, β-phenylpropionic, phenoxyacetic, and trans-cinnamic acid. The reactions of 3-fluoro- (or chloro-) or 4-methyl-biphenyl-4′-carboxylic, and of 9-X-10-anthroic acids (X = Me, Cl, or Br) were also studied similarly. The Hammett polar susceptibility constant, ρ, has been calculated for each set of reactions. The values of ρ are discussed in terms of transmission of electronic effects through the side-chain by a field effect, and for side-chains conjugated with the ring, by a π-electron effect, both of which are inversely proportional to the first power of the distance of the carbonyl group from the ring.