The phosphodiesters of 4,4’-methylenebis(3-hydroxy-2-naphthoic acid) (4) and 3-carboxy-2,2’-dihydroxy-diphenylmethane (5) are constrained into a cyclic structure such that the oxygens of the two o-carboxy groups of 4 and the single o-carboxy group of 5 have restricted stereospecific positions with an o-CO2- oxygen to phosphorus distance of 3.7 Angstrom. In the hydrolysis of 4, P-31 NMR and HPLC data show the existence of an intermediate cyclic acyl phosphate in the g,g conformation. The O-18 isotopic effects on P-31 chemical shifts show incorporation of two O-18 atoms in the product H3PO4. This observation is consistent with intramolecular o-CO2- nucleophilic attack on phosphorus to provide an acyl phosphate intermediate which undergoes hydrolytic cleavage by HO-/(HO-)-O-18 attack on phosphorus (one O-18 incorporation) to provide a phosphate monoester which also undergoes hydrolysis with a second O-18 incorporation on phosphorus. For hydrolysis of 4, the pH vs log k(obsd) profile, the values of the deuterium solvent kinetic isotope effect, and the activation entropy accord a mechanism which involves intramolecular attack of o-CO2- on the phosphate phosphorus assisted by the o-CO2H as a general acid catalyst, The latter can involve o-CO2H hydrogen bonding to the -(PO2-)- oxygen(s) and/or leaving phenolic oxygen. At neutrality, 4 hydrolyzes ca. 10(4) fold faster than 5 which only has one o-carboxy group and 10(8)-10(9)-fold faster than diphenyl phosphate.