A mechanistic study of thioester hydrolysis with heavy atom kinetic isotope effects.

The carbonyl-C, carbonyl-O, and leaving-S kinetic isotope effects (KIEs) were determined for the hydrolysis of formylthiocholine. Under acidic conditions, 13kobs = 1.0312, 18kobs = 0.997, and 34kobs = 0.995; for neutral conditions, 13kobs = 1.022, 18kobs = 1.010, and 34kobs = 0.996; and for alkaline conditions, 13kobs = 1.0263, 18kobs = 0.992, and 34kobs = 1.000. The observed KIEs provided helpful insights into a qualitative description of the bond orders in the transition state structure.