That point in the chemical reaction at which the reactants (i.e., chemical entities about to react with each other) have been “brought to the brink.” It is a point in the chemical reaction process in which an “activated condition” is reached. From this point the probability of the reaction going to completion and producing a product is very high. The transition state separates (energetically) products from reactants. It is viewed as being at the top of the energy barrier separating reactants and products. The reacting species in the transition state can, because of their location at the “top” of the energy barrier, “fall” to either products or reactants.