Category: Pericyclic Reactions

The last class of concerted pericyclic reactions that we will consider is the groups of reactions known as sigmatropic rearrangements. In a sigmatropic rearrangement, a σ bond in a molecule is broken, a new σ bond is formed and the π electrons rearrange. The σ bond that breaks is bonded to an allylic carbon. It…

In a cycloaddition reaction, the orbitals of one molecule must overlap with the orbitals of the second molecule. Therefore, the frontier molecular orbitals of both reactants must be evaluated to determine the outcome of the reaction. Since the new σ bonds in the product are formed by donation of electron density from one reactant to…

In a cycloaddition reaction, two different π-bond-containing molecules react to form a cyclic molecule. The reverse process is known as cycloreversion or retro-cycloaddition. The Diels-Alder reaction is one of the best known examples of a cycloaddition reaction. Cycloaddition reactions are classified according to the number of π electrons that interact in the reaction. The Diels-Alder reaction…

In 1965 R.B. Woodward, an experimentalist, and Ronald Hoffmann, a theorist, developed the conservation of orbital symmetry theory to explain electrocyclic reactions. This theory explains the relationship among the structure and configuration of the reactant, the conditions (thermal and /or photochemical) under which the reaction takes place and the configuration of the product. The overlap of p orbitals to…

The original explanation of Woodward and Hoffmann (1965, 1970) involved generating a so-called ‘orbital correlation diagram’ for the reaction under consideration, and then carrying out the reaction in such a manner that the symmetries of the reactant and product orbitals matched exactly. This enables a correlation diagram for the reaction to be constructed, according to…

An electrocyclic reaction is an intramolecular reaction that involves the concerted formation of a sigma bond between the two ends of a linear conjugated π (pi) system, or the reverse reaction in which the sigma bond in a cyclic reactant is broken to produce a linear conjugated π system. The product in cyclic compound has…

Organic reactions can be classified into three major classes: polar reactions (reaction between nucleophile and electrophile), radical reactions (reaction using one electron from each of the reactants) and pericyclic reactions. A pericyclic reaction, that is, cyclic reorganization of electrons, is one in which bonds are made or broken in a concerted cyclic transition state. A…