In polar reaction the electrons move in pairs. This is a thermodynamic property, it tells nothing about how fast equilibrium is established, only the final mixture. In any reaction, an energy change must occur since the overall energy required to break all necessary bonds rarely equals energy given off by forming new bonds. Reaction Profiles Consider changes in the structure of a system as a reaction proceeds. The structure of the TS is important because it tells us about how a reaction occurs.
Some reactions have more than one step between each step an intermediate is involved.
Isotope Effects Deuterium is the isotope of H with mass 2. Not always Look at Hammond postulate. The structure of a transition state resembles the structure of the closest stable species. Reactive Intermediates short lived species that are never present in high conc because they react as quickly as they are formed. Carbocations trivalent carbon bearing a positive charge Electron donating groups can stabilize positive charge.