STEPWISE VERSUS CONCERTED MECHANISMS AT TRIGONAL CARBON - TRANSFER OFTHE 1,3,5-TRIAZINYL GROUP BETWEEN ARYL OXIDE IONS IN AQUEOUS-SOLUTION

Displacements of 4-nitrophenolate ions from 2-(4-nitrophenoxy)-4,6-dim ethoxy-1,3,5-triazine by substituted phenolate ions in aqueous solutio n obey a linear Bronsted-type equation, log k(Aro) = 0.951pK(a) - 10.9 8, over a range of pK(a) values greater than and less than the pK(a) o f the leaving phenol. The absence of curvature is consistent with a me chanism involving a single transition state. This conclusion is suppor ted 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 re action of 3,4-dinitrophenolate ion with the (3,3-dinitrophenoxy)triazi ne is calculated to have a Kreevoy-Albery tau value of 1.04, indicatin g that in this case changes in effective charge on entering and leavin g ligands are approximately balanced.