Which of the following is the most stable conformation of $2_{\text{-}}\text{butene}$?

• A. Trans conformation, where the two methyl groups are on opposite sides of the double bond
• B. A conformation where both methyl groups are eclipsed
• C. Cis conformation, where the two methyl groups are on the same side of the double bond
• D. A conformation with one methyl group and one hydrogen on the same side

Answer: (A)

Verified step by step guidance

1. Identify the structure of 2-butene, which has a double bond between the second and third carbon atoms, and two methyl groups attached to these carbons.
2. Understand that the stability of alkene conformations depends largely on steric hindrance and torsional strain between substituents around the double bond.
3. Recall that in alkenes, rotation around the double bond is restricted, so the terms 'cis' and 'trans' describe the relative positions of substituents across the double bond: 'cis' means substituents on the same side, 'trans' means on opposite sides.
4. Compare the steric interactions in the cis and trans conformations: in the cis conformation, the two bulky methyl groups are on the same side, causing steric repulsion, while in the trans conformation, the methyl groups are on opposite sides, minimizing steric hindrance.
5. Conclude that the trans conformation is more stable because it reduces steric strain by placing the two methyl groups opposite each other, leading to lower overall energy.