One of the conceptually simpler molecular changes into which an @[email protected] can be notionally dissected. Such changes include bond rupture, bond formation, internal rotation, change of @[email protected] or bond @[email protected], bond @[email protected], redistribution of charge, etc. The concept of primitive changes is helpful in the detailed verbal description of elementary reactions, but a primitive change does not represent a process that is by itself necessarily observable as a component of an @[email protected]