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Open Chain and Closed Chain Conformations

Learning Objective: To study the common names of open-chain and closed-chain conformations and their stability. 

Skill Level - Intermediate

Prerequisites: 

 

Chapter: Stereochemistry

Sub-topic: Conformational Isomerism

 

Author's Note: Once you learn how to draw the conformations, it then becomes necessary to identify various open-chain and closed-chain conformations. How exactly does one structure differ from the other, and why do molecules adopt only some conformations? Here, you will also come across their names, which you will frequently encounter in your study of conformations in organic chemistry.

Open Chain and Closed Chain Conformations

Open-Chain 

Staggered and eclipsed are two common conformations shown by open-chain systems. They are obtained by rotating the proximal (front) or distal (back) carbon atom by 60 degrees. 

For example, in case of two-carbon ethane, an eclipsed conformation occurs when the front C-H bonds eclipses or hides the back C-H bonds. The angle between the front H-C-C plane and the back C-C-H plane is 0o.

 

 

The staggered conformation is when the hydrogen atom....

.

.

The angle between two planes, XCC and CCY, that separates the substituents of the front with the distal carbon is called the dihedral angle or the torsion angle. 

Molecules prefer staggered conformation for two reasons....

 

Angle of torsion and energy barrier

.......This barrier to rotation is called the torsional barrier of the single bond....

 

Closed-Chain Conformations

Unlike their open-chain counterparts, closed-chain cycloalkanes have restricted rotation due to being held, out of necessity, at a fixed bond angle....

 

Subscribe to learn all about conformations, their names, structures, and why, despite their flexibility, they decided to adopt a fixed form. 

 

Stereochemistry
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Stereoisomerism - Conformation and Configurational Isomerism

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