Comments on: Staggered vs Eclipsed Conformations of Ethane

By: Conformational Isomers of Propane | Straight A Mindset

Conformational Isomers of Propane | Straight A Mindset — Thu, 07 Dec 2023 21:54:04 +0000

[…] the previous post [see: Staggered vs Eclipsed Conformations of Ethane] we saw that ethane has two important conformational isomers, depending on the orientation of the […]

By: Staggered vs Eclipsed Conformations of Ethane | Straight A Mindset

Staggered vs Eclipsed Conformations of Ethane | Straight A Mindset — Thu, 07 Dec 2023 21:51:18 +0000

[…] Recap: The Tetrahedral Structure of Methane (CH4) […]

By: Dr Prasanna Kumar Sharma

Dr Prasanna Kumar Sharma — Fri, 28 Oct 2022 13:28:28 +0000

Thanks for the material

By: Daniel

Daniel — Wed, 17 Aug 2022 17:14:41 +0000

Praise the Sun :D

By: James Ashenhurst

James Ashenhurst — Wed, 17 Aug 2022 17:10:56 +0000

In reply to Daniel. Thank the

By: Daniel

Daniel — Wed, 17 Aug 2022 16:14:18 +0000

Ok, thanks, now I understand :)
So “we” are indeed adding energy to this system :)

By: James Ashenhurst

James Ashenhurst — Wed, 17 Aug 2022 16:11:38 +0000

In reply to Daniel.

At absolute zero (0 K ) there would be no energy available and the molecule would be locked in a staggered conformation that it would not be able to get out of.
At 0K all molecular motion stops.
As temperature increases, more thermal energy becomes available, and as molecules collide and rotate there will eventually become sufficient energy for the molecule to break out of the shallow potential energy “well” of 3 kcal/mol and assume other conformations.
To make a long story short, at room temperature, a good rule of thumb is that there is about 20 kcal/mol of thermal energy available for reactions to happen at a reasonable rate.
So at room temperature there is more than sufficient energy available for the C-C bond of ethane to be in constant rotation between the eclipsed and staggered conformations.

By: Daniel

Daniel — Wed, 17 Aug 2022 15:39:21 +0000

Yes, but why?
I gave reasons why it should prevent rotation.
Let’s assume that one molecule was in eclipsed conformation and then shift to staggered conformation(if that’s possible)
How this molecule can return to eclipsed formation? It requires energy.
Where this energy come from?
If we are not adding any external energy to system then, over time all molecules should be in staggered conformation. That means this difference should prevent rotation, and yet it doesn’t. Why is that?

By: James Ashenhurst

James Ashenhurst — Wed, 17 Aug 2022 02:24:59 +0000

In reply to Daniel. You are correct that the energy difference does *not* prevent rotation. At any given time the population of molecules in the staggered conformation will be higher than those for molecules in the eclipsed conformation because it is lower energy by about 3 kcal/mol.

By: Daniel

Daniel — Tue, 16 Aug 2022 18:49:24 +0000

Why exactly the energy difference between these conformations doesn’t prevent rotation?
Because:
If molecules want to have lowest possible energy then over time staggered conformation should win, over time all molecules should have this conformation.
Assuming, of course, we are not adding any energy to the system.

If so, any difference, no matter how small, should prevent rotation.