Table of Contents
What is the difference between axial and equatorial?
The key difference between axial and equatorial position is that axial bonds are vertical while equatorial bonds are horizontal.
Is equatorial more stable or axial?
A conformation in which both substituents are equatorial will always be more stable than a conformation with both groups axial.
How do you know when to use axial or equatorial?
Why is equatorial favored over axial?
6.10A). Because diastereomers have different energies, one form is more stable than the other. Equatorial methylcyclohexane is more stable than axial methylcyclohexane. In fact, it is usually the case that the equatorial conformation of a substituted cyclohexane is more stable 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 is axial less stable?
Both chair conformations have one axial substituent and one equatorial substituent. According to the guideline, the conformer with the larger substituent in equatorial is more stable because if the large group is axial, a stronger steric strain will be generated and it is less stable.
Which position axial or equatorial is more favorable?
Are wedges equatorial or axial?
In all cases, a substituent that was marked by a wedge or a dash in a 2-D drawing will remain that way, but in the chair conformation, the wedge might means axial “up” instead of equatorial “up” depending on whether it is a right- or left-handed chair.
Does axial have more energy than equatorial?
Note that in the conformation where methyl is axial, there is a gauche interaction between the axial methyl group and C-3. This is absent in the conformation where methyl is equatorial. This gauche interaction is an example of van der Waals strain, which is what makes the axial conformer higher in energy.
Are lone pairs axial or equatorial?
Lone pairs of electrons generally prefer to occupy equatorial positions rather than axial positions. The justification for this preference, according to VSEPR theory, is that the lone electron pairs are more repulsive than bonding electron pairs, and thus the lone pairs prefer the less crowded equatorial positions.
Is equatorial position 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.
Which chair conformation is higher in energy?
The most stable conformation of methylcyclohexane is the chair conformation in which the methyl group is equatorial. The alternative chair conformation, in which the methyl group is axial, is 7.3 kJ/mol higher in energy.
What is the most stable conformation?
hydrocarbons. …with respect to the other—the eclipsed conformation is the least stable, and the staggered conformation is the most stable. The eclipsed conformation is said to suffer torsional strain because of repulsive forces between electron pairs in the C―H bonds of adjacent carbons.
What chair conformation is least stable?
If the tert-butyl group is placed in the axial bond, then the chair has the highest energy, or the least stable conformation.
Which chair conformation is lowest in energy?
In the chair conformation , all the hydrogens are staggered. You can see this by rotating the model to look down the carbon-carbon bonds. The chair is the lowest energy conformation for cyclohexane.
Do wedges mean up or down?
Wedge: A symbol used to indicate the position of a bond or group relative to the plane of the paper or screen. A solid wedge indicates this bond or group is projecting out towards the viewer. A broken (hashed) wedge indicates this bond or group is receding away from the viewer.
How do you make a chair conformation more stable?
To Determine Chair Conformation Stability, Add Up The A-Values For Each Axial Substituent. The Lower The Number, The More Stable It is.
What is a chair flip?
Ring flip (chair flip): The conversion of one cyclohexane chair conformation into another, by rotation around single bonds. Cyclohexane ring flip causes axial substituents to become equatorial, and equatorial substituents to become axial.
Why do lone pairs prefer equatorial positions?
Lone pair repulsion is greater than bond pair repulsion. Therefore, to attain stability, the lone pairs should be kept at a position farthest from each other, so they occupy the equatorial positions.
Which repulsion is strongest?
- Greatest repulsion is between 2 lone pairs.
- Followed by repulsion between one lone pair and one bonding pair.
- The weakest repulsion is between 2 bonding pairs, the magnitude of repulsion between bonding pairs of electrons depends on the EN difference between a central atom and the other atoms.