Structure-reactivity relationships in the pyridinolysis of N-methyl-N-arylcarbamoyl chlorides in dimethyl sulfoxide

Nucleophilic substitution reactions of N-methyl-N-arylcarbamoyl chlorides (YC6H4N(CH3)COCl) with pyridines (XC5H4N) have been investigated in dimethyl sulfoxide at 45.0 degreesC. A striking trend in the selectivity parameters is that they are constant within experimental errors, rho (X) = -2.25 +/- 0.03, beta (X) = 0.42 +/- 0.01, and rho (Y) = 1.10 +/- 0.06, with changing reactivities of the electrophiles (delta sigma (Y)) and nucleophiles (delta sigma (X)), respectively, and this leads to a vanishingly small cross-interaction constant, rho (XY) approximate to beta (XY) approximate to 0. The rate data can be expressed in the Ritchie N+ type equation. Based on this and other results, the mechanism of nucleophile (pyridine) addition to the resonance- stabilized carbocation is proposed. It has been shown from the definition of beta (XY) (and rho (XY)) together with the Marcus equation that the high intrinsic barrier, DeltaG(0)(double dagger), in the intrinsic-barrier controlled reaction series is a prerequisite for such reactions in which the cross-interaction vanishes and the N+ relationship holds.