Stepwise Versus Concerted Mechanisms at Trigonal Carbon - Transfer Of The 1,3,5-Triazinyl Group Between Aryl Oxide Ions In Aqueous-Solution

Displacements of 4-nitrophenolate ions from 2-(4-nitrophenoxy)-4,6-dimethoxy-1,3,5-triazine by substituted phenolate ions in aqueous solution obey a linear Bronsted-type equation, log k(Aro) = 0.951pK(a) - 10.98, over a range of pK(a) values greater than and less than the pK(a) of the leaving phenol. The absence of curvature is consistent with a mechanism involving a single transition state. This conclusion is supported by the existence of cross-correlation effects (p(xy) = 0.0561) on beta(nuc) of the pK(a) of the leaving group and on beta(1g) of the pK(a) of the nucleophile on beta(1g). The value of beta(eq), the Bronsted selectivity for transfer of the triazinyl function between phenolate ions, is calculated from the Bronsted data to be 1.48. The identity reaction of 3,4-dinitrophenolate ion with the (3,3-dinitrophenoxy)triazine is calculated to have a Kreevoy-Albery tau value of 1.04, indicating that in this case changes in effective charge on entering and leaving ligands are approximately balanced.