When a chair-flip of any generic cyclohexane is performed, what happens to the groups positions?
A. up and down switch, axial and equatorial also switch.
B. up and down stay the same, axial and equatorial stay the same.
C. up and down switch, axial and equatorial stay the same.
D. up and down stay the same, axial and equatorial switch.
The Correct Answer and Explanation is :
The correct answer is A: up and down switch, axial and equatorial also switch.
Explanation:
A chair flip is a conformational interconversion of a cyclohexane ring that results in a new chair conformation. During this process, the atoms in the cyclohexane ring undergo a sequence of bond rotations that effectively “flip” the ring. As a result of this flip, the spatial positions of substituents attached to the cyclohexane also change.
Key Observations:
- Axial and Equatorial Positions Switch:
- In the original chair conformation, substituents alternate between axial (positions pointing straight up or down, perpendicular to the plane of the ring) and equatorial (positions pointing outwards, roughly parallel to the plane of the ring).
- After a chair flip, substituents that were axial become equatorial, and those that were equatorial become axial.
- Up and Down Positions Switch:
- The “up” or “down” designation is relative to the cyclohexane ring’s plane.
- For example, if a substituent is “up” in the axial position in the original conformation, it will still be “up” but in the equatorial position after the flip.
- Net Effect of the Chair Flip:
- Both the axial/equatorial and up/down positions switch. This means the spatial environment of the substituents changes, potentially altering their steric interactions and strain in the molecule.
Example:
Consider methylcyclohexane. If the methyl group starts in the axial “up” position:
- After the flip, it will move to the equatorial “up” position.
- Both its axial/equatorial and up/down properties have switched.
This phenomenon is a cornerstone of understanding the dynamics and stability of cyclohexane conformations. Substituents often prefer the equatorial position to minimize steric hindrance, which is crucial in stereochemical and conformational analysis.