Which of the following best describes the lowest energy chair conformation of $\text{cis-1-ethyl-2-isopropylcyclohexane}$?

• A. Both the ethyl and isopropyl groups are on the same side of the ring, with one group axial and the other equatorial.
• B. Both the ethyl and isopropyl groups are on opposite sides of the ring, with both groups equatorial.
• C. Both the ethyl and isopropyl groups are on the same side of the ring, with both groups axial.
• D. Both the ethyl and isopropyl groups are on opposite sides of the ring, with one group axial and the other equatorial.

Answer: (A)

Verified step by step guidance

1. Identify the substituents and their positions on the cyclohexane ring: an ethyl group at carbon 1 and an isopropyl group at carbon 2.
2. Recall that 'cis' means both substituents are on the same side of the ring, so both groups must be either both up or both down relative to the ring plane.
3. Draw the cyclohexane chair conformation and place the substituents at carbons 1 and 2, considering that one will be axial and the other equatorial in one chair form.
4. Flip the chair conformation to see the alternative arrangement where the axial substituent becomes equatorial and vice versa, keeping the cis relationship intact.
5. Compare the steric interactions and 1,3-diaxial interactions in both conformations to determine which has the lowest energy, typically favoring the conformation where the bulkier group is equatorial.