Final answer:
The equatorial conformation of trans-1,3-diethylcyclohexane is more stable than the axial conformation due to lower steric strain, making statement (c) the correct description.
Step-by-step explanation:
The chair conformations of trans-1,3-diethylcyclohexane involve different arrangements of the ethyl groups attached to the cyclohexane ring. In one conformation, the ethyl groups can be in the equatorial positions, whereas in the flipped form, these groups are in the axial positions. Comparing the stability of these two conformations, the equatorial conformation is more stable than the axial conformation. This is due to steric strain in the axial conformation, where the ethyl groups experience 1,3-diaxial interactions with other axial hydrogen atoms on the same side of the ring, leading to increased steric repulsion and instability. Consequently, the statement (c) The equatorial conformation is more stable than the axial conformation correctly describes the chair conformations of trans-1,3-diethylcyclohexane.
The chair conformations are not at the same energy level because the steric strain associated with axial substituents increases the energy of that conformation. Additionally, it is important to note that chair conformations are rapidly interconverting at room temperature, which means that the cyclohexane ring flip occurs frequently, allowing both axial and equatorial positions to be sampled by all substituents over time. However, due to the reasons already explained, the majority of molecules at any given moment will be in the more stable equatorial conformation.