Rank the following conformers of the isomers of 1-ethyl-2,4-dimethylcyclohexane from most to least stable with 1 being the most stable and 4 being the least stable. Explain A, B, C, D.

When ranking the conformers of 1-ethyl-2,4-dimethylcyclohexane, we need to consider the sterics of the substituents on the cyclohexane ring. Conformers can be affected by the positions of bulky groups, which can lead to steric hindrance or strain.

Stability Ranking:

1. 1. Conformer A: This is typically the most stable conformation, as it has the largest substituents (ethyl and methyl groups) in the equatorial positions. Equatorial positions minimize steric interactions as they extend outward from the ring.
2. 2. Conformer B: This conformation may have one bulky group in the axial position, causing some steric strain. However, it’s still more stable than configurations with multiple axial substituents.
3. 3. Conformer C: This conformation places two bulky groups in axial positions, leading to increased steric hindrance and 1,3-diaxial interactions, which destabilize the molecule significantly.
4. 4. Conformer D: This is the least stable conformation, likely because it has the most sterically hindered arrangement, with all bulky substituents in axial positions causing maximum 1,3-diaxial interactions.

The key to ranking these conformers lies in the orientation of the ethyl and methyl groups. Placing larger groups in equatorial positions greatly reduces steric strain, which directly affects the overall stability of the conformer.