The key difference between exocyclic and endocyclic double bond is that one carbon atom of the exocyclic double bond is in the ring structure and the other carbon atom is located outside the ring structure whereas two carbon atoms of the endocyclic double bond are in the ring structure.
Exocyclic and endocyclic double bonds are parts of chemical compounds which are cyclic or ring structures. These two double bonds differ from each other according to the location of the two carbon atoms that are involved in the formation of the double bond.
CONTENTS
1. Overview and Key Difference
2. What is an Exocyclic Double Bond
3. What is an Endocyclic Double Bond
4. Side by Side Comparison – Exocyclic vs Endocyclic Double Bond in Tabular Form
5. Summary
What is an Exocyclic Double Bond?
Exocyclic double bonds are covalent chemical bonds which contain two carbon atoms bonded to each other via a sigma bond and a pi bond. This type of double bonds has one of the two carbon atoms in the ring structure. We can observe exocyclic double bonds only in unsaturated organic compounds (unsaturated compounds are chemical compounds having either double bonds or triple bonds). Specifically, these covalent bonds can be observed in alkenes.
Figure 01: Chemical Structure of Methylenecyclohexane
The name exocyclic refers to the presence of the double bond external to the cyclic structure. But this double bond is still connected to the cyclic structure via one of the two double-bonded carbon atoms. It is very important to recognize exocyclic double bonds form endocyclic double bonds when naming a chemical compound using the IUPAC nomenclature method. An example of a chemical compound containing an exocyclic double bond is methylcyclohexane.
What is an Endocyclic Double Bond?
Endocyclic double bonds are covalent chemical bonds that contain two carbon atoms bonded to each other via a sigma bond and a pi bond (the composition of a double bond). These covalent chemical bonds have both carbon atoms of the double bond in the ring structure. In other words, both carbon atoms of the endocyclic double bond are members of the cyclic structure.
Figure 02: Chemical Structure of Cyclopentene
An example of a chemical compound containing an endocyclic double bond is cyclopentene. Cyclopentene contains an endocyclic double bond since both double-bonded carbon atoms are members of the cyclic structure. It is very important to recognize exocyclic double bonds form endocyclic double bonds when naming a chemical compound using the IUPAC nomenclature method.
What is the Difference Between Exocyclic and Endocyclic Double Bond?
Exocyclic and endocyclic double bond are parts of cyclic structures which differ from each other according to the location of the double bond. The key difference between exocyclic and endocyclic double bond is that one carbon atom of the exocyclic double bond is in the ring structure and the other carbon atom is located outside the ring structure whereas two carbon atoms of the endocyclic double bond are in the ring structure.
Below infographic summarizes the differences between exocyclic and endocyclic double bond in tabular form.
Summary – Exocyclic vs Endocyclic Double Bond
Exocyclic and endocyclic double bond are parts of cyclic structures which differ from each other according to the location of the double bond. The key difference between exocyclic and endocyclic double bond is that one carbon atom of the exocyclic double bond is in the ring structure while the other carbon atom is located outside the ring structure whereas two carbon atoms of the endocyclic double bond are in the ring structure.
Reference:
1. “3.6: Alkenes.” Chemistry LibreTexts, Libretexts, 11 Aug. 2020, Available here.
Image Courtesy:
1. “Methylenecyclohexane” By Edgar181 – Own work (Public Domain) via Commons Wikimedia
2. “Cyclopentene-2D-skeletal” Von Benjah-bmm27 – Eigenes Werk (Gemeinfrei) via Commons Wikimedia
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