Is cis always Equatorial?
It is important to remember that the bonds on a given side of a chair ring-conformation always alternate in this fashion. Therefore, it should be clear that for cis-1,2-disubstitution, one of the substituents must be equatorial and the other axial; in the trans-isomer both may be equatorial.
Is cis axial or equatorial more stable?
In cis-1,2-dimethylcyclohexane, one methyl group is axial and one methyl group is equatorial in both ring flip conformers, so neither conformer is more stable than the other.
Why are equatorial substituents more stable?
Consequently, substituted cyclohexanes will preferentially adopt conformations in which the larger substituents are in the equatorial orientation. When the methyl group is in the equatorial position this strain is not present which makes the equatorial conformer more stable and favored in the ring flip equilibrium.
What does cis mean in chair conformations?
[…] For the case where the two groups are on the same side of the ring, we refer to it as ‘cis’ (from the Latin, meaning, “same side of”.) For the case where the two groups are on the opposite side of the ring, we refer to it as “trans” (meaning “opposite side of’”). […]
How do you identify a cis trans isomer?
Consider the longest chain containing the double bond: If two groups (attached to the carbons of the double bond) are on the same side of the double bond, the isomer is a cis alkene. If the two groups lie on opposite sides of the double bond, the isomer is a trans alkene.
Is axial or equatorial lower in energy?
When we do this, here’s what we find. Instead of being equal, the ratio of “equatorial methyl” to “axial methyl” conformers is about** 95:5 favouring the conformation where the methyl group is equatorial. Very interesting! This must mean that the equatorial conformation is of lower energy than the “axial” conformation.
Which chair conformation is most stable?
The most stable conformation of cyclohexane is the chair form shown to the right. The C-C-C bonds are very close to 109.5o, so it is almost free of angle strain. It is also a fully staggered conformation and so is free of torsional strain.
Why are equatorial bonds more stable?
Substituents prefer equatorial rather than axial positions in order to minimize the steric strain created of 1,3-diaxial interactions. The more stable conformation will place the larger substituent in the equatorial position.
What affects the relative stability of two different chair conformers for a cyclohexane with one substituent?
Both chair conformations have one axial substituent, and one equatorial substituent. According to the guideline, the conformer with larger substituent in equatorial is more stable because if the large group is axial, stronger steric strain will be generated and it is less stable.