Draw the two chair conformations of each compound, and label the substituents as axial and equatorial. In each case, determine which conformation is more stable.
a. cis-1-ethyl-2-isopropylcyclohexane
b. trans-1-ethyl-2-isopropylcyclohexane

Verified step by step guidance

1. Start by drawing the basic chair conformation of cyclohexane. This involves drawing two parallel lines that represent the carbon backbone, with alternating axial and equatorial positions for substituents.
2. For cis-1-ethyl-2-isopropylcyclohexane, place the ethyl group at carbon 1 and the isopropyl group at carbon 2. Since the compound is cis, both substituents should be on the same side of the ring. Assign one substituent to an axial position and the other to an equatorial position, then switch them for the second conformation.
3. Label the substituents in each conformation as axial or equatorial. Remember that axial positions are perpendicular to the ring plane, while equatorial positions are roughly parallel to the ring plane.
4. Evaluate the stability of each conformation. Generally, the conformation with the larger substituent in the equatorial position is more stable due to reduced steric hindrance.
5. Repeat the process for trans-1-ethyl-2-isopropylcyclohexane. In this case, the substituents should be on opposite sides of the ring. Draw both chair conformations, label the substituents, and determine which conformation is more stable based on the positions of the substituents.

Key Concepts

Chair Conformation

Chair conformation is a three-dimensional shape that cyclohexane rings adopt to minimize steric strain and torsional strain. In this conformation, carbon atoms are staggered, reducing repulsion between hydrogen atoms. Understanding how to draw and interpret chair conformations is crucial for analyzing the stability of cyclohexane derivatives.

Axial and Equatorial Positions

In a chair conformation, substituents on the cyclohexane ring can occupy axial or equatorial positions. Axial positions are perpendicular to the ring plane, while equatorial positions are roughly parallel. Substituents in equatorial positions generally experience less steric hindrance, making them more stable than those in axial positions.

Cis and Trans Isomerism

Cis and trans isomerism refers to the relative orientation of substituents around a cyclohexane ring. In cis isomers, substituents are on the same side of the ring, while in trans isomers, they are on opposite sides. This orientation affects the stability and spatial arrangement of the chair conformations, influencing which conformation is more stable.