Localized M.O.s

In addition to being equivalent to the classical bonds, localized M.O.s are useful in understanding chemical reactions, and other phenomena which take place slowly relative to the speed of light: i.e., phenomena which take place in 10^-12s or slower.

Consider a S_N² reaction. All the bonds forming and breaking can be seen in the localized M.O.s. Consider the reactive sites in a molecule (double bonds, lone pairs, etc.). These have exact equivalents in the localized M.O.s. The energies of localized M.O.s are indicative of the reactivity of the associated electron pair. Consider an excited, insulating polymer, such as excited polyethylene. The excited state is usually written with an asterisk (*), and is generated simply by localizing the M.O.s of an excited polymer cluster.