Which of the following substituted $\mathrm{cyclohexanes}$ is most stable?

• A. $\text{trans-1,4-dimethylcyclohexane}$ with both methyl groups in axial positions
• B. $\text{cis-1,3-dimethylcyclohexane}$ with one methyl group axial and one equatorial
• C. $\text{trans-1,2-dimethylcyclohexane}$ with both methyl groups in equatorial positions
• D. $\text{cis-1,2-dimethylcyclohexane}$ with both methyl groups in axial positions

Answer: (C)

Verified step by step guidance

1. Identify the conformations of cyclohexane and understand that substituents prefer the equatorial position over the axial position due to steric hindrance and 1,3-diaxial interactions.
2. Analyze each given substituted cyclohexane by determining the positions (axial or equatorial) of the methyl groups in their most stable chair conformations.
3. Recall that trans-1,4-dimethylcyclohexane with both methyl groups axial will experience significant steric strain due to 1,3-diaxial interactions, making it less stable.
4. Consider cis-1,3-dimethylcyclohexane with one methyl axial and one equatorial; this mixed positioning reduces steric strain compared to both axial but is still less stable than both equatorial.
5. Recognize that trans-1,2-dimethylcyclohexane with both methyl groups equatorial minimizes steric hindrance and 1,3-diaxial interactions, making it the most stable conformation among the options.