 In contrast, the thin notion of a reaction mechanism focuses on a discrete set of steps. In each step, a set of reactive intermediates are generated. These intermediates are quasi-stable molecular species that will ultimately yield the products of the reaction. For example, the much studied biomolecular nucleophilic substitution (SN2) reaction is said to have a single reactive intermediate with the incoming nucleophile and outgoing leaving group both partially bonded to the reactive carbon center (see Figure 6). Such a description of the reaction mechanism is not only abstract in that it leaves out much detail, but it is also highly idealized. Reactions do not take actually place as a series of discrete steps, each of which generates a quasi-stable reaction intermediate.