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Steric Strain Vs. Torsional Strain

I am not quite getting the difference between those two. Any detailed explanation would be highly appreciated.


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Steric strain is the strain resulting from non bonded atoms being forced too close together (more specifically, to within the regions of one another's Van der Waal radii, hence the alternative name of this sort of strain; "Van der Waals strain").

Tosional strain is the resistance to bond twisting.
This refers to the tendency for some molecules to stay in the anti-periplanar conformation, as opposed to having relatively free rotation around the single bond. This is generally due to bulky groups vicinal to one another, or can be to cancel any dipoles that may exist in the syn- or gauche- conformations.
(edited 9 years ago)
Original post by Infraspecies
Steric strain is the strain resulting from non bonded atoms being forces too close together (more specifically, to within the regions of each other's Van der Waals radii, hence the alternative name of this sort of strain "Van der Waals strain).

Tosional strain is the resistance to bond twisting.
This refers for the tendency for some molecules to stay in the anti-periplanar conformation, as opposed to having relatively free rotation around the single bond. This is generally due to bulky groups vicinal to one another, or can be to cancel any dipoles that may exist in the syn- or gauche- conformations.

Thank you!

But, honestly, I still don't feel confident. What is the exact difference between them? Both are caused due to repulsion of electron clouds right? When the molecule is in the staggered conformation, and when it is in the eclipsed form, what is the difference in the steric strain between them? Shouldn't it be constant.

strain.PNG98.7KB
Original post by Daniel Atieh
Thank you!

But, honestly, I still don't feel confident. What is the exact difference between them? Both are caused due to repulsion of electron clouds right? When the molecule is in the staggered conformation, and when it is in the eclipsed form, what is the difference in the steric strain between them? Shouldn't it be constant.



As I said, steric strain is due to two groups being closer together than is stable, due to repulsive interactions.

Torsional strain can be caused by this, if it prevents rotation around a single bond. Torsional strain is generally represented as a free energy diagram, plotting potential energy against dihedral angle. Higher barriers result in torsional strain. However, it can be caused by other things too.

As for the difference in steric strain between eclipsed and staggered conformations; if I have butane, are the terminal CH3's closer together if the molecule is staggered, or eclipsed? Steric strain correlates with proximity.
Original post by Infraspecies
As I said, steric strain is due to two groups being closer together than is stable, due to repulsive interactions.

Torsional strain can be caused by this, if it prevents rotation around a single bond. Torsional strain is generally represented as a free energy diagram, plotting potential energy against dihedral angle. Higher barriers result in torsional strain. However, it can be caused by other things too.

As for the difference in steric strain between eclipsed and staggered conformations; if I have butane, are the terminal CH3's closer together if the molecule is staggered, or eclipsed? Steric strain correlates with proximity.

It sort of makes sense now. Thanks!

They are closer together in the eclipsed form right? So the torsional strain will cause them to move to the staggered conformer. Now Steric strain exist in both situations right?

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