Question

Which statement is NOT true?

A. The structure of the transition state is between the structures of the reactants and products

B. The activation energy for a one-step reaction is equal to the energy difference between the energy of the reactants and the energy of the transition state.

C. the transition state structure always resembles the starting materials more closely than it resembles the products

D. in the transition state, the bonds that break and form are partially broken or partially formed, respectively.

E. the transition state is more similar in structure to the species that it is closer to energetically

Answer 1

Statement C is not correct. According to Hammond's postulate, that says: “If two states, as, for example, a transition state and an unstable intermediate, occur consecutively during a reaction process and have nearly the same energy content, their interconversion will involve only a small reorganization of the molecular structures”. This means that species with similar energies along the reaction will also have similar structures. So when a reaction happens in a way that the TS appears early, it is more closely in energy to the reactants and it will resemble them, BUT, if the TS appears later it will be more closely resembling the energy of the products, so it will have a structure more similar to them. The postulate allows us to accurately predict the shape of a reaction coordinate diagram and also in predicting the shape and structure of the TS

Examples are: an exothermic reaction, where the transition state is closer to the reactants than to the products in energy. Therefore, the transition state resembles the reactants. Or in an endothermic reaction, the transition state is closer to the products than to the reactants in energy, so according to Hammond’s postulate, in an endothermic reaction the transition state resembles the products.