Draw cis-1-ethyl-4-methylcyclohexane in its lowest energy conformation.
The Correct Answer and Explanation is :
To draw cis-1-ethyl-4-methylcyclohexane in its lowest energy conformation, we must understand the cyclohexane ring and how substituents are positioned on it. Cyclohexane rings are typically drawn as chair conformations, which are the most stable because they minimize steric strain.
Steps to Draw the Conformation:
- Identify the substituents:
- The ethyl group is attached at carbon 1.
- The methyl group is attached at carbon 4.
- The “cis” part of the name means that both substituents are on the same side of the ring (either both axial or both equatorial).
- Draw the chair conformation of cyclohexane:
- Begin by drawing the chair conformation of cyclohexane, which is a six-membered ring with alternating axial and equatorial bonds. Axial positions are vertical (up or down), and equatorial positions are roughly horizontal.
- Position the substituents:
- In a cis conformation, the substituents must be on the same side of the ring. For the lowest energy conformation, both the ethyl and methyl groups should be in equatorial positions because bulky groups are more stable in the equatorial position due to less steric hindrance.
- Optimize the conformation:
- Place the ethyl group at the equatorial position on carbon 1 and the methyl group at the equatorial position on carbon 4. This minimizes steric strain since the bulky substituents are not in close proximity.
- If either group were in the axial position, it would cause 1,3-diaxial interactions, which increase steric strain and make the conformation less stable.
Final Conformation:
- Ethyl group at the equatorial position on carbon 1.
- Methyl group at the equatorial position on carbon 4.
This arrangement minimizes the steric interactions, making it the lowest energy conformation.
Explanation:
The chair conformation is the most stable for cyclohexane due to the fact that all carbon-hydrogen bonds are staggered. When substituents like an ethyl or methyl group are placed in the axial positions, steric clashes occur with other axial hydrogens, known as 1,3-diaxial interactions, which increase strain. Placing the substituents in the equatorial positions minimizes these interactions, leading to a lower energy, more stable conformation.