The key difference between Endo and Exo Diels Alder compounds is that the Endo Diels Alder product has its substituents on the same face of the bridged ring system whereas the Exo Diels Alder product has its substituents on the opposite faces of the bridged ring system.
Endo-Exo isomerism is a special type of isomerism that falls into the category of stereoisomers. We can find this isomerism in organic compounds having a substituent on its bridged ring system. Endo and Exo are prefixes that we use to name an organic compound according to the locations of this substituent. Chiefly, we use these prefixes with the products of Diels Alder reaction. The product of this type of reaction is usually a substituted cyclohexene derivative.
CONTENTS
1. Overview and Key Difference
2. What is Endo Diels Alder
3. What is Exo Diels Alder
4. Side by Side Comparison – Endo vs Exo Diels Alder in Tabular Form
5. Summary
What is Endo Diels Alder?
Endo Diels Alder product is an organic compound having the substituents on the same face of the bridged ring system. A Diels Alder reaction forms six-membered rings; thus we call it a cycloaddition. In the formation of endo product through this reaction, the substituents combine with each other via a bridged ring system in which the substituents are in the same face. Therefore, it has the maximum overlap between their faces.
Figure 01: Endo and Exo Structures in Diels Alder Reactions
The resulting endo product of this reaction has a “C-shape”. Moreover, this structure has the maximum strain between the substituents. Thus, the formation of the endo product during a Diels Alder reaction has a less chance.
What is Exo Diels Alder?
Exo Diels Alder product is an organic compound having the substituents on the opposite faces of the bridged ring system. A Diels Alder reaction forms six-membered rings; thus we call it a cycloaddition. In the formation of exo product via this reaction, the substituents combine with each other via a bridge ring system having the substituents in opposite faces. Therefore, it has a minimal overlap between the faces of the ring system. Moreover, this product has an “Z-shape”.
What is the Difference Between Endo and Exo Diels Alder?
Endo Diels Alder product is an organic compound having the substituents on the same face of the bridged ring system while exo Diels Alder product is an organic compound having the substituents on the opposite faces of the bridged ring system. This is the key difference between endo and exo Diels Alder. Furthermore, the endo Diels Alder has a C-shape whereas the exo Diels Alder has a Z-shape. Moreover, the endo product shows a maximum strain due to the maximum overlap between its faces. However, the exo product shows a minimal strain due to the minimum overlap between its faces.
The below infographic presents the difference between endo and exo Diels Alder in tabular form for quick reference.
Summary – Endo vs Exo Diels Alder
The Diels Alder reaction in organic chemistry is the most common cycloaddition reaction. It can give two major products; endo product and exo product. The difference between endo and exo Diels Alder compounds is that the endo Diels Alder product has its substituents on the same face of the bridged ring system whereas the exo Diels Alder product has its substituents on the opposite faces of the bridged ring system.
Reference:
1. “Exo vs Endo Products In The Diels Alder: How To Tell Them Apart.” Master Organic Chemistry RSS. Available here
Image Courtesy:
1.”Diels-Alder-Endo-and-exo-orientation”By Mazhe2 – en.wikipedia, (Public Domain) via Commons Wikimedia