Comments on: Cyclohexane Chair Conformation Stability: Which One Is Lower Energy?

By: Bredt’s Rule (And Summary of Cycloalkanes) | Straight A Mindset

Bredt’s Rule (And Summary of Cycloalkanes) | Straight A Mindset — Thu, 07 Dec 2023 22:15:22 +0000

[…] A-values are additive. With di- and trisubstituted cyclohexanes, we can use A-values to determine which chair conformation is most stable. […]

By: Cyclohexane Chair Conformation Stability: Which One Is Lower Energy? | Straight A Mindset

Thu, 07 Dec 2023 22:11:52 +0000

[…] A-Values Are A Useful Measure of Bulkiness […]

By: Maha

Maha — Sun, 01 Jan 2023 21:14:02 +0000

It was really helpful thanks a lot

By: James Ashenhurst

James Ashenhurst — Wed, 12 Aug 2020 16:56:36 +0000

In reply to Shiwei Liu.

Yes! That is an excellent point. This is addressed in Reference 3. The gauche interaction in trans 1,2-dimethylcyclohexane is 0.74 kcal/mol. https://www.sciencedirect.com/science/article/abs/pii/S0040403900814355

By: Shiwei Liu

Shiwei Liu — Sat, 01 Aug 2020 05:39:48 +0000

The equatorial substituents including methyl group can also have significant gauche interactions with each other. For example, the two equatorial methyl groups in trans-1,2-dimethylcyclohexane (equatorial conformation). The gauhe interaction between these two methyl group is 0.9 kCal/mol instead of zero kCal/mol in this post. Below includes more examples for your reference.

https://sites.science.oregonstate.edu/~gablek/CH334/Chapter4/bare_Problem_LG9.htm

By: Andrea

Andrea — Tue, 19 Nov 2019 10:28:11 +0000

Thank you. Great work with your blog!

By: James Ashenhurst

James Ashenhurst — Mon, 18 Nov 2019 18:50:21 +0000

Hi Andrea! Alluding to your earlier comment, there is likely a solvent effect because of differences in dipole moment. From Eliel’s “Stereochemistry of Organic Compounds”, page 673 I see that the dipole moment of cis 1,2-dichlorocyclopropane is 3.10 and the dipole moment of the trans is 2.63 . This would suggest that in less polar solvents (e.g. pentane, hexane) the trans would be favored so as to minimize the dipole moment.
I seem to recall some discussion of the solvent dependence of A-values from one of Eliels papers but I can’t find it at the moment!

By: Andrea

Andrea — Mon, 18 Nov 2019 18:33:13 +0000

In March’s organic chemistry (7th edition chapter 4) is pointed out that for 1,2-dihalides cyclohexanes there is a preference for the diaxial form. Why not the equatorial?

By: Andrea

Andrea — Mon, 18 Nov 2019 08:27:52 +0000

What about the effect of different solvents on the stabilization for substituted cyclohexane?

By: Sourav

Sourav — Sun, 13 Oct 2019 01:04:10 +0000

Thank you so much for the explanation!
I seem to have pondered too much over the molecule as I have another question.
Will there be van der Waals strain in the case of bulky equatorial groups lying distant from one another, say in 1,3 or 1,4 positions? Will the diaxial conformer still be favoured?