The simple molecular orbital theory is introduced into the field of chemical reactions, and the symmetry of the reaction molecular orbital and the product molecular orbital is used to demonstrate the nature of symmetry permission (occurrence) and symmetry prohibition (non-occurrence) of the synergistic reaction in which the reaction molecular bond breaks and the product molecular bond is generated at the same time, which is called Woodward-Hoffman rule.

Introduction:

In 196s, some ideas of "conservation of molecular symmetric orbits" put forward by American organic chemists R．B． Woodward and R. Hoffman were formulated, which made them universally recognized. The simple molecular orbital theory is introduced into the field of chemical reactions, and the symmetry of reaction molecules and product molecular orbitals is used to demonstrate the nature of symmetry permission (occurrence) and symmetry prohibition (non-occurrence) of the synergistic reaction of simultaneous reaction molecular bond breakage and product molecular bond formation, which is called Woodward-Hoffman rule. For any synergistic reaction, the occupied orbits of all reactants must be the same as those of their related products, otherwise the reaction cannot occur. In the elimination reaction of removing one molecule of amine when quaternary ammonium salt reacts with alkali, the olefins produced mainly come from alkyl groups with fewer substituents.