Which of the following is the most stable conformation of $\text{trans-1-isopropyl-3-methylcyclohexane}$?

• A. The isopropyl group is $\text{equatorial}$ and the methyl group is $\text{axial}$
• B. Both the isopropyl and methyl groups are in $\text{axial}$ positions
• C. Both the isopropyl and methyl groups are in $\text{equatorial}$ positions
• D. The isopropyl group is $\text{axial}$ and the methyl group is $\text{equatorial}$

Answer: (C)

Verified step by step guidance

1. Identify the substituents on the cyclohexane ring: an isopropyl group at carbon 1 and a methyl group at carbon 3, with a trans relationship between them.
2. Recall that in cyclohexane chairs, bulky groups prefer the equatorial position to minimize 1,3-diaxial interactions, which cause steric strain.
3. Since the substituents are trans, one will be axial and the other equatorial in one chair conformation; in the other chair flip, their positions will switch.
4. Compare the steric effects of having the larger isopropyl group axial versus equatorial; the isopropyl group is bulkier than the methyl group, so it prefers equatorial to reduce steric hindrance.
5. Conclude that the most stable conformation is the one where both the isopropyl and methyl groups occupy equatorial positions, which corresponds to the trans relationship with the isopropyl equatorial and methyl equatorial after considering the ring flip.