Learning Objective: To get familiar with conformational isomerism, what it means, how it occurs, and also differs from other forms of isomerism.
Skill Level - Beginner
Prerequisites:
- Single and double bond rotation (Chapter - Covalent Bond)
- Bond angle
- Interelectronic repulsions, energy change, and stability relationship
- Degree of freedom of a molecule in solid, liquid, and gaseous state
Chapter: Stereochemistry
Sub-topic: Conformational Isomerism
Author's Note: Since most of organic chemistry talks about covalently bonded molecules, it becomes highly important to understand how different covalently bonded structures, especially those containing single bonds, may be differentiated. Even though the bond attachments may look similar, the structures may still be different, and all these conditions are covered in the name of isomerism, which belongs to the category of stereochemistry.
Conformational isomerism mainly deals with single-bond-containing structures. This section introduces the concept and then proceeds to their representation, nomenclature, stability, and importance.
Conformational Isomerism - Introduction
Organic molecules are pretty flexible. They can bend, rotate, spin, collide, vibrate, and change shape, even though most of these events are not invisible.
One such unseen act that is significant to organic chemistry is the rotation of atoms around the single bonds.
This causes the molecules to adopt various spatial arrangements or shapes and easily interconvert between shapes by bond rotations.
The atoms holding the other bond types, that is, double and triple bonds, are rigid. If one tries to rotate such a bond, it will break, so they don’t entertain such prohibited practices of bond rotation. For that reason, it is an absolute privilege of the single bonds to show conformations, and a specific conformation is called a conformer or conformational isomer.
(Related Definition - Conformation)
Many such conformational isomers are undoubtedly interconvertible by single-bond rotations. So, these isomers are simply different rotational (or structural) arrangements of the same molecule and, therefore, non-separable.
Let us look at our own body as an example. We can adopt standing and sitting positions, which are easily reversed by rotating our hip and knee joints.
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But in larger molecules like in two-carbon ethane, keeping one carbon end fixed and rotating along the C-C bond (sp3-sp3) leads to many possible arrangements. The angle separating the front and back carbon substituents may vary by a large number, like....
Such a high barrier for bond rotations would make it more difficult...
Conformations may even change depending on the state....
Next: How are Conformational Isomers Depicted?
Next: Open-chain and Closed-Chain Conformations
Next: Conformational Isomerism - Nomenclature Related to single and double bond rotations
Next: Conformational Analysis - Factors affecting the stability of conformers
Next: Importance of Conformational Analysis
Next: Conformation in Compounds with Lone Pair
Next: Role of Solvents in Conformational Isomerism
Next: An Example of Conformation Dependent Reaction and Product Selectivity
