The rate coefficients for the esterification with diazodiphenylmethane in ethanol at 30" and the pK, values at 25" of a number of ortho-substituted trans-cinnamic, phenoxyacetic, 3-phenylpropionic, ortho-, meta-, and para-substituted cis-and trans-cr-phenylcinnamic acids have been determined. The effects of substitution have been assessed by a Hanimett-type correlation. A comparison of the transmission of the polar effects of ortho and metalpara substituents indicates the prime importance of the field effect, augmented where possible by ax-inductive effect. A reversed dipolar substituent field effect has been detected for the cis-ortho-substituted cinnamic acids.Canadian Journal of Chemistry, 46. 3909 (1968) Introduction In a search for model systems to distinguish between the inductive and field effects (1, 2), a previous analysis (3) suggested that for certain reaction and substituents, the polar effect of ortho-substituents in benzoic acids is transmitted approximately twice as efficiently as that of metalpara-substituents. A very simple test presents itself. If the field effect is the main means of transmission, the ratio will decrease and approach unity as the substituted phenyl group becomes more distant from the reaction site. This is due to the field effect varying with cos 0/r2 for a point dipole (4), where r is the distance from the dipole and the reaction site and 0 is the angle between r and the dipole. However, if an inductive effect is mainly responsible, the ratio will remain the same. This is because the inductive effect decreases by a factor E for each intervening link (2,5).In this study, the reactivities of a series of ortho-substituted trans-cinnamic, phenoxyacetic, 3-phenylpropionic, cis-and traiw-ci-phenylcinnamic acids in their ionization and their reaction with diazodiphenylmethane in ethanol have been studied, together with the metalpara-substituted a-phenylcinnamic acids. The ortho-substituted -systems have been correlated by a Hammett-type equation and compared with the

The rate coefficients for the reaction with diazodiphenylmethane in methanol, ethanol, isopropyl alcohol, t-butyl alcohol, 2-methoxyethanol, 2-n-butoxyethanol, dimethyl sulfoxide, ethyl acetate, and toluene at 30" and the pK, values in water, 50% ethanol-water, and 80% 2-methoxyethanol-water of 18 substituted acetic and propionic acids have been determined. A further 14 acids have been studied to a more limited extent. The effect of substitution has been estimated by linear free energy relations. The reaction constants for the ionization reaction are almost independent of the medium. This is interpreted as being due to the field effect of the proximate polar substituents passing through the molecular cavity almost alone. The occurrence of steric inhibition of solvation causing acid weakening for bulky multisubstitution is confirmed. The reaction constants for the esterification reaction are affected by the solvent. This is attributed to dependence on solvation of the transition state.Canadian Journal of Chemistry, 46, 2929 (1968) IntroductionAs part of our examination of the mode of the transmission of polar effects, it was considered important that transmission in aliphatic systems and their dependence on the medium should be studied. Suitable reactions were considered to be the esterification of carboxylic acids with diazodiphenylmethane (DDM) and their ionization. The system chosen for this study was a series of singly substituted acetic and 3-substituted propionic acids, together with a number of more highly substituted acids. The intention was to obtain a comprehensive series of results for the esterification and ionization reactions for this model system in order to be able to discuss the influence of the substituents on reactivity in aliphatic systems.Taft in his pioneering studies (1) made a distinct advance in understanding polar substituent effects in aliphatic systems. The aliphatic polar substituent constants, a*, which had been separated from the accompanying steric effects in ester hydrolysis, were found to correlate, among other reactions, the ionization of aliphatic carboxylic acids in water at 25" (1) and the esterification of the acids with DDM in ethanol at 25" (2). Hoefelmeyer and Hancock (3) and Bowden, Chapman, and Shorter (4) have extended these correlations to the esterification of aliphatic

SEVERAL investigations have been made to by a field effect operating through the transmissive distinguish between the inductive and the field cavity. The molecular structures of these models effects for the transmission of polar substituent involve the bonds that could transmit the effect effects.1 Unfortunately, the results for most inductively being contained in the low dielectric model systems studied can be explained by both cavity which would transmit the field effect. inductive transmission through the bonds con-However, the field effect of a dipolar substituent necting the substituent to the reaction site and has an angular dependence2 which is not involved

The rate coefficients for the reaction with diazodiphenylmethane in methanol, ethanol, isopropyl alcohol, t-butyl alcohol, 2-methoxyetl1anol, 2-11-butoxpetlianol, and ethyl acetate at 30' and the pK, values in 80% 2-n-butoxyethanol-water of a series of 9-substit~~ted 10-anthroic and 8-substituted 1-naphtlioic acids have been determined. The effect of substitution has been analyzed by linear free energy relations. The variation in the susceptibilities of the systems to polar substituent effects \\.it11 the medium are examined. The occurrence of reversed dipolar substituent effects in the reactions of the I ,S-naphthoic acids is detected. The inlplications of the results for the inductive and field effect models for the transmission of polar effects are discussed.

A series of 9-substituted 10-triptoic acids have been prepared. Their pKa values in 80% 2-methoxy-ethanol–water and 50% ethanol–water at 25° and rate coefficients for esterification with diazodiphenyl-methane in five alcohols at 30° have been measured. The results have been analyzed by linear free energy relations. The π-inductive effect is shown to be unimportant in such systems, while the field effect model can account for the transmission.