Organic Chemistry Chapter 3 Part III Reaction Equilibrium

Organic Chemistry Chapter 3 Part III Reaction Equilibrium vs. Reaction Rates Nanoplasmonic Research Group

Two Perspectives for a Given Reaction Thermodynamics: Whether the reaction does go or not Kinetics: If yes, How fast ?

How to Predict How Fast ? ? • Past – The Arrhenius equation – Empirical observation and ignores any mechanistic considerations, such as whether one or more reactive intermediates are involved in the overall conversion of a reactant to a product • Transition State Theory – Intermediate vs. Transition state – Elementary Reaction

Reaction Energy Diagram (I) • The Hammond Postulate – If two states, for example a transition state and an intermediate, occur consecutively during a reaction process and have nearly the same energy, their inter conversion will involve only a small reorganization of molecular structure • How to interpret the postulate – Effectively, the postulate states that the structure of a transition state resembles that of the species nearest to it in free energy – That is to say that the transition state of an endothermic reaction resembles the products, while that of an exothermic reaction resembles the reactants

Reaction Energy Diagram (II) • Curtin-Hammett Principle – In a chemical reaction that yields one product from one conformer/reactant and a different product from another conformer/reactant (and provided these two conformers/reactants are rapidly interconvertible relative to the rate of product formation), the product composition is controlled by the difference in free energies of the respective transition states

Reaction Energy Diagram (III) • The Principle of Microscopic Reversibility – For reversible thermal reactions, the same pathway that is followed in the forward direction of a reaction will be followed in the reverse direction