Which of the following is the most stable conformation of $\mathrm{cis}-1-\mathrm{ethyl}-3-\mathrm{isopropyl}\mathrm{cyclohexane}$?

• A. Both ethyl and isopropyl groups are in axial positions on the cyclohexane ring.
• B. Ethyl group is axial and isopropyl group is equatorial on the cyclohexane ring.
• C. Ethyl group is equatorial and isopropyl group is axial on the cyclohexane ring.
• D. Both ethyl and isopropyl groups are in equatorial positions on the cyclohexane ring.

Answer: (D)

Verified step by step guidance

1. Identify the substituents on the cyclohexane ring and their positions: an ethyl group at carbon 1 and an isopropyl group at carbon 3, with a cis relationship between them.
2. Recall that in cyclohexane, substituents prefer the equatorial position over the axial position due to reduced steric strain and 1,3-diaxial interactions.
3. Since the substituents are cis, they must be on the same face of the ring. This means if one substituent is axial, the other must be axial or equatorial depending on the ring flip.
4. Draw or visualize the chair conformations to determine which arrangement places both substituents in equatorial positions simultaneously, considering the ring flip.
5. Conclude that the most stable conformation is the one where both the ethyl and isopropyl groups occupy equatorial positions, minimizing steric hindrance and strain.