Predicting unexpected chemical reactions by isopotential searching

The reactions of a chemical system are dictated by the corresponding potential energy surface (PES). Since reasonably accurate PESs are now available from quantum chemical calculations, a great deal of chemistry can, in principle, be predicted using existing techniques. We describe a few algorithms for finding low-energy exit channels from a well in a PES without foreknowledge of the products. Several illustrative applications are provided, including (1) unimolecular rearrangement of benzocyclohex-1-en-3-yne and (2) bimolecular reaction between ammonia and dichlorosilane. These two systems were chosen because their reactions were previously found to have been predicted incorrectly. In both cases, the correct mechanisms are recovered using isopotential searching strategies.