Like minima, the first order saddle points are stationary points with all forces zero. Strictly speaking, a transition state of a chemical reaction is a first order saddle point. Transition states correspond to saddle points on the potential energy surface. The saddle point is the point of highest energy along the reaction path and is also the point of lowest energy in the direction perpendicular to the reaction path (lowest point of the ridge that separates reactants and products. The highest point on this path is the col, or saddle point that separates the reactant basin from the product basin.
Like a group of tired mountain climbers, the reactant molecules in the transition state theory will follow a unique path that connects the reactant basin and the product basin. They will seek out a gorge that takes them over the ridge. Such mountain climbers will seek out the easiest path, one that avoids steep climbs and raises minimally in altitude.
The simplest versions of the transition state theory assume that reactants behave like very tired mountain climbers who are trying to get from one valley to another and have to cross a mountain range. Instead, a simplified approach, termed the transition state theory, is commonly employed. However, such a complete description is challenging because of the need to map out a multidimensional potential energy surface. A complete description of a chemical reaction dynamics would include all these paths. Reactant molecules that have lots of energy could follow a path that involves high energy configurations, reactants with less energy will follow a path that involves configurations with lower energy. For polyatomic molecules, there is an enormously large number of possible rearrangement paths that take reactants to products. Transition States Chemical Reactions Transition StatesĬhemical reactions occur by the rearrangement of nuclear configurations from the reactant state to the product state. Transition States in Chemical Reactions: Tutorial and Assignments
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