Minimum Change of “Shapes” of Molecular Orbitals in the Elementary Chemical Reactions and a New Perspective of Quantum Chemistry

Chemical substances are highly diverse. Here, we discuss the regularities of chemical changes among the substances. As a typical example, the regularity of the change between benzene and its structural isomers, i.e. Dewar benzene and prismane, has been discussed in terms of molecular vibrational theory and orbital correlation diagrams. It has been shown that when a certain molecule changes to another one with a similar structure, the “shapes” of the original electronic states are transferred to the next ones with minimum change. Regarding this, it has been pointed out that Neumann-Wigner’s non-crossing rule need not be applied to orbital correlation diagrams. It has also been shown that changes of molecules are “quantized” and cannot be described continuously, i.e. the states which can be accurately described by the Schrödinger equation are limited to “quantum steady states”.