52374-04-6Relevant articles and documents
Concerted displacement mechanism at trigonal carbon: the aminolysis of 4-aryloxy-2,6-dimethoxy-1,3,5-triazines
Shakes, Janice,Raymond, Christel,Rettura, Donatella,Williams, Andrew
, p. 1553 - 1558 (2007/10/03)
4-Aryloxy-1,3,5-triazines undergo bimolecular nucleophilic displacement reactions with amines and pyridines to yield the 4-substituted triazine and aryloxide ion.Rate constants in aqueous solution for the bimolecular reaction of morpholine and 4-dimethylaminopyridine with the title ethers obey the Hammett ? evaluation with Hammett ρlg values 1.65 and 0.82, respectively.Comparison of the ρlg values with the Hammett ρeq for the equilibrium constants indicates that build-up of effective charge on the departing ether oxygen in the transition structures is less than half of that for complete bond fission.Rate constants for the reaction of substituted pyridines with the 4-nitro- and 3,4-dinitro-phenyl ethers obey Broensted equations with exponents βnuc of 0.68 and 1.06, respectively.The build-up of effective charge in bond formation is greater than half of that expected for complete bond formation.Variation in βnuc and ρlg as a function of leaving group and nucleophile structure, respectively, is consistent with substantial coupling between bond forming and bond breaking.The ratio of the Leffler exponents in the pyridinolysis reactions, αnuc/αlg, is greater than unity, consistent with an imbalance between bond fission and bond formation and indicating an accumulation of negative charge in the heteroaromatic nucleus in the transition structure 29percent of that expected for adduct formation.
