Intramolecular General Acid Catalysis of Phosphate Transfer. Nucleophilic Attack by Oxyanions on the PO32- Group

摘要: Phosphate transfer from the 8-dimethylammonium-naphthyl-1-phosphate monoanion 4m to water and a range of nucleophiles shows general acid catalysis by neighboring NH+ group, through strong intramolecular hydrogen bond. Reactivity is insensitive charge on nucleophile, so that fluoride oxyanions displace dimethylaminonaphthol PO32- group as effectively do amines same basicity. (predictably) relatively basicity nucleophile α-effect. A bond present in product, but also reactant, evidenced major perturbations pKa's phosphate dimethylamino groups, 3.94 9.31, respectively, ab initio calculations. Rate accelerations are order 106-fold despite this stabilization:  strength evidently significantly enhanced transition state. The evidence suggests it depends remarkably strongly deg...