Hammond's postulate

Hammond's postulate suggests that in a chemical reaction, the structure of a transition state (the high-energy state during a reaction) resembles the structure of the nearest stable species—either the reactants or products—depending on which is closer in energy. If the reaction is slow and the transition state is near the reactants in energy, it looks more like reactants. If the reaction is fast and the transition state is closer in energy to the products, then it resembles the products. This idea helps chemists predict reaction pathways and how quickly reactions will occur based on the structures involved.