What are electrocyclic reaction? 

Electrocyclic reactions are a class of pericyclic reactions in organic chemistry where a ring system undergoes reorganization through the breaking and forming of σbonds in a concerted manner. These reactions involve the rearrangement of the π electrons within a cyclic compound. Electrocyclic reactions can be classified into two main types: ring-opening (electrocyclic ring-opening) and ring-closing (electrocyclic ring-closing) reactions.

In a ring -opening electrocyclic reactions, a cyclic compound undergoes cleavage of one more σ bonds to form an open - chain compound. This usually results in the formation of a conjugated diene or polyene system.

In contrast , ring-closing electrocyclic reactions involve the closure of a ring by  the formation of one or more σ bonds. This trypically leads to the formation of a cyclic compound.

These reactions are characterised by their concerted mechanism, meaning that the breaking and forming of bonds occurs simultaneously in single step without the formation of any intermediates. The stereo chemistry of the product is often governed by the woodward-Hoffmann rules, which provide guidelines for predicting the stereochemical outcome based on the symmetry properties of the reacting molecules.

An electrocyclic reaction is the concerted cyclization of a conjugated π-electron system by converting one π-bond to a ring forming σ-bond. The reverse reaction may be called electrocyclic ring opening. Two examples are shown on the right. The electrocyclic ring closure is designated by blue arrows, and the ring opening by red arrows. Once again, the number of curved arrows that describe the bond reorganization is half the total number of electrons involved in the process.

An electrocyclic reaction is the concerted cyclization of a conjugated π-electron system by converting one π-bond to a ring forming σ-bond. The reverse reaction may be called electrocyclic ring opening. Two examples are shown on the right. The electrocyclic ring closure is designated by blue arrows, and the ring opening by red arrows. Once again, the number of curved arrows that describe the bond reorganization is half the total number of electrons involved in the process.

Electrocyclic reactions are a type of chemical reaction where the structure of a molecule changes by forming or breaking a ring of atoms, specifically through the rearrangement of electrons in conjugated systems (systems with alternating double and single bonds). These reactions are a subset of pericyclic reactions and occur in a single, concerted step, meaning all changes happen simultaneously without any intermediate steps.