CSIR-NET Chemical Science: Short Notes on Pericyclic Reactions!

By Neetesh Tiwari|Updated : June 8th, 2021

Are you looking for some short and reliable notes during your CSIR UGC NET preparations? Then, you have come to a perfect place!

Candidates preparing for their CSIR UGC NET exam might need to get some short study notes and strategies to apply while preparing for the key exam of their life. At this point in time, We at BYJU'S Exam Prep come up with short notes on the Pericyclic Reactions, which come under the part, i.e., Organic Chemistry of the Chemical Science syllabus. 

Our experienced subject-matter experts have meticulously designed this set of short notes for Pericyclic Reactions to give you the most standard set of study materials to focus upon. In this cut-throat competitive world, students need to prepare themselves with the best study materials to help them learn and for their future. Here we are offering the best study notes that are reliable and can be used by the students during their preparations for the upcoming CSIR-NET 2021 exam.

 Pericyclic Reactions

A pericyclic reaction follows a concerted type mechanism and proceeds through a cyclic transition state. These reactions take place in the presence of either light or heat and are completely stereospecific, i.e., a single stereoisomer of the reactant will form a single stereoisomer of the product. Pericyclic reactions are of two types: electrocyclic reactions and cycloadditions. 


Electrocyclic Reaction:

It is a reversible reaction that involves ring closure or ring opening.

  • In a ring closure electrocyclic reaction, there is the formation of a cyclic product that contains one more σ bond and one fewer π bond than the reactant.



  • In a  ring-opening electrocyclic reaction, a σ bond of a cyclic reactant is cleaved to form a conjugated product having more than one π bond.



Cycloaddition Reaction:

A cycloaddition is an intermolecular reaction in which compounds having π bonds form a cyclic product with two new σ bonds.



Diels–Alder reaction: A thermal [4 + 2] cycloaddition occurs between a diene with four π electrons and a dienophile with two π electrons.

Note: (4 and 2 refer to the number of π electrons).



Photochemical reaction: It is a  [2 + 2] cycloaddition between two alkenes, each having two π electrons, and it results in the formation of cyclobutane. 

Note: Thermal [2 + 2] cycloadditions do not take place.



Molecular Orbitals

MO theory considers bonds as the mathematical combination of atomic orbitals that forms a new set of orbitals called molecular orbitals (MOs). Ethylene π molecular orbitals.



Two p orbitals can combine in two different ways and result in the formation of a π bonding molecular orbital (designated as ψ1)  and a π* antibonding molecular orbital (designated as ψ2*).


Advantages of Pericyclic Reactions:

  • Less probability of formation of unwanted side products since these reactions are unaffected by the influence of solvent or any reagent). 
  • The reaction is highly stereospecific in nature because of concerted orbital symmetry.
  • Variety of applications in biosynthesis. 
  • This reaction is also a non-conventional energy source, e.g., the conversion of cyclobutane to two ethylene molecules is accompanied by the release of heat.


Download PDF for Short Notes on Pericyclic Reactions


Also Read : 

 CSIR NET Chemical Science - Short Notes on Organometallic Compounds

 CSIR NET Chemical Sciences: Short Notes on Soft Acid-Base Concept!

CSIR-NET Chemical Science: Short Notes on Molecular Spectroscopy


~ Keep Upvote this article and share it among your friends.

→ If you have any questions feel free to ask in the comments section below.

Also, subscribe to our Youtube Channel for daily Live Classes for CSIR NET 2021.

Best of Luck!!
Sahi Prep hai to Life Set Hai!!
Go BYJU'S Exam Prep


write a comment

Follow us for latest updates