RATIONAL VS RANDOM PARAMETERS IN TRANSITION-STATE MODELING - MM2 TRANSITION-STATE MODELS FOR INTRAMOLECULAR HYDRIDE TRANSFERS

An MM2 force field to model transition states of intramolecular hydride transfers from alkoxides to carbonyl compounds has been developed. On the basis of ab initio geometries of transition structures, the force field reproduces activation energies in a series of intramolecular hydride transfers. A previous force field based upon a similar philosophy reported by Menger and Sherrod gave a poor correlation; this has been found to be due to an abnormally large oxygen van der Waals term that was incorporated into the parameter set. An argument is presented for the use of rational, rather than random, parameters to study organic reactions.