The remote label method was used to measure primary and secondary 18O isotope effects in the alkaline hydrolysis of O, O-diethylphosphorylcholine iodide (DEPC) and the primary 18O effect in the alkaline hydrolysis of O, O-diethyl-m-nitrobenzyl phosphate (DE m NBP). Both the leaving group of interest (choline or m-nitrobenzyl alcohol) and ethanol can be ejected during hydrolysis due to the similarity of their p K values. The heavy-atom isotope ...