Bifurcating Surfaces One TS, Two Products

Motion along the reaction coordinate away from the TS will lead to lower energy structures. If one follows the reaction coordinate in the forward or reverse directions, eventually one will reach a critical point. Usually, these two critical points (the one located in the reverse direction and the one found in the forward direction) are local minima, and so we say that the TS connects reactant with product Most importantly, there is a 1 1 correspondence between TS and product, or TS and reactant. 

Singleton carried out a combined experimental/computational/MD study of the enyne-allene cyclization problem. First, he determined that the experimental KIE for the cyclization of 60 is 1.43. This value is smaller than that usually found for concerted ene reactions, where kg/kjj is often greater than 

Trajectories were initiated at either the TS 63 or a random sampling of structures about this TS. Most trajectories reach a product, either 62 or 64 within 30 fs, and all finished within 85 fs. These short trajectories suggest little opportunity for IVR to occur. Most of the trajectories, 72 out of 101, end up at 62, the product that is directly connected to the TS. The other 29 trajectories terminate at 64. Some of these trajectories were allowed to go on for another 100 fs but none exited the area about 64. Given sufficient time, these trajectories would cross over the barrier about 65 and make the final product 62. The upshot is that the diradical is produced even though there is no TS that takes reactant into it. The ridge provides the opportunity for trajectories to fall into two possible energy sinks. Most follow the steepest descent downhill toward 62, but some will divert into the neighboring minimum, the diradical 64. 

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