Cis/Trans, Axial/Equatorial Question

[ojyarumaru]

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Which is more stable?

trans-1-bromo-3-methylcyclohexane
OR
cis-1-bromo-3-methylcyclohexane

I drew the chair conformation out for both and I get the trans conformation as bromine axial up and CH3 equatorial down, cis conformation as both groups equatorial down. I thought equatorial was more stable than axial, but I also know that trans is usually more stable than cis? Which one takes precedence in this case?

Sorry if this is a noob question haha and thanks in advance!

 

[jhanago]

Cis

 

[Nontrad37]

Trans alkenes are more stable than cis alkenes because of less steric repulsion from large substitute groups.

Other than this, which is more stable all depends on the context.

In this case, two equatorial positions would put the two bulky groups the farthest apart. In addition, equatorial position has the least steric interaction with other axial protons on the ring.

 

[RSD2014]

Which is more stable?

trans-1-bromo-3-methylcyclohexane
OR
cis-1-bromo-3-methylcyclohexane

I drew the chair conformation out for both and I get the trans conformation as bromine axial up and CH3 equatorial down, cis conformation as both groups equatorial down. I thought equatorial was more stable than axial, but I also know that trans is usually more stable than cis? Which one takes precedence in this case?

Sorry if this is a noob question haha and thanks in advance!

With cis-1-bromo-3-methylcyclohexane we can place both substituents in EQUATORIAL for lowest energy (more stable).


With trans-1-bromo-3-methylcyclohexane , one substituent will be Axial, one substituent will be Equatorial...higher energy than cis-1-bromo-3-methylcyclohexane, thus less stable.

 

[ojyarumaru]

Thanks!

 

[27Teeth]

remember that when you draw the "trans" conformation the Methyl group must be placed in the more stable equatorial position. A methyl group which is 4 atoms is MUCH larger than Br so it must be placed in the equatorial spot.
(However, remember that the general rule is that atoms with a higher MW are usually favored for the equatorial position. e.g. I>Br) 😀