The highest state of energy in the process of transforming the reactant system into the product system
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Transition state refers toreactantThe highest energy state (or calledActivated complex）[1]。The state of transition bond is that the old bond is not completely broken and the new bond is not completely formed.The transition state is unstable and cannot be separated.The energy difference (△ E) between the transition state and the reactant is calledactivation energy。Different reaction systems have different activation energies, and the greater the activation energy, the more difficult the reaction will be.
The transition state is the molecular configuration corresponding to the highest energy point in the reaction coordinate of the elementary reaction.Molecules in transition state are also called activated complexes.Theoretically, the activated complex is extremely unstable, and the probability of its transformation to reactants and products is equal;[1] AbsoluteIrreversible reactionIn the transition state, all colliding molecules will be converted into products.[2] According toquantum mechanicsIn theory, the population of the activated complex is zero, and the transition state is the highest energy point. Any disturbance will lead to its change, so it cannot be separated or observed.
The concept of transition state is important for understandingOrganic reaction mechanismIt plays an important role.Transition state theoryIt is believed that chemical reaction can be completed not by simple collision of reactant molecules, but when the reactant reachesProductIn the course of the process, it passes through a high energy transition state.This is similar to mountain climbing. The highest point of the mountain is the transition state.The transition state is an unstable combination of reactant atoms, which can be quickly decomposed into products in irreversible reactions.usuallyReaction intermediateIt is difficult to distinguish between the energy of and the transition state.With the help offemtosecond infrared spectrumThe molecular configuration structure near the transition state has been observed.
