Ortho Effect. I.

Abstract

The cumulative ortho effect observed in the ionization of substituted benzoic acids was discussed. It was pointed out that the nature of the cumulative ortho effects observed in 3, 4-, 2, 4-, 2, 5-, 2, 3-, and 2, 6-disubstituted benzoic acids varied and was distinguishable from each other. It has been demonstrated that the cumulative ortho effect involves various functions, such as the susceptibility for the substituent effects on the interaction between ortho substituents, the substituent effects itself on the interaction, the interaction itself, and in some cases, a combination of them. It was suggested that in the ionization of benzoic acids, the direct field effect between the point charge on the reacting group and the dipole of the ortho substituent was responsible for the ortho effect. Closer approach of the reacting group toward the 2-substituent which might be effected by introducing a second substituent into the 3- or 6-position of the 2-substituted benzoic acids would invert the direction of the dipole toward the point charge on the reacting group, and would therefore cause another ortho effect in a direction opposite to that of the usual acid strengthening ortho effect. Actually, this hypothesis has been supported by a number of examples.