Molecular orbitals are critical in the rationalization of several chemical reactions.
Thus, the frontier molecular orbital theory, proposed by Fukui's group, postulated
the importance of the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied
Molecular Orbital (LUMO) for chemical reactions. It should be kept in mind,
however, that there are limitations of this theory and new perspectives about the chemical
reactivity have recently been arisen based on composition and location of other frontier
molecular orbitals. In this review, we have reported the development and the most recent
applications of the Frontier Effective-for-Reaction Molecular Orbital (FERMO) concept,
which describes the breaking and formation of new chemical bonds and can in turn, provide
important clues that modulate chemical reactivity of atoms and molecules.