Draw the two chair conformations of each of the following substituted cyclohexanes. In each case, label the more stable conformation.]
c. cis-1-ethyl-4-isopropylcyclohexane
d. trans-1-ethyl-4-methylcyclohexane

Verified step by step guidance

1. Identify the substituents on the cyclohexane ring. For cis-1-ethyl-4-isopropylcyclohexane, the substituents are an ethyl group at carbon 1 and an isopropyl group at carbon 4. For trans-1-ethyl-4-methylcyclohexane, the substituents are an ethyl group at carbon 1 and a methyl group at carbon 4.
2. Draw the basic chair conformation of cyclohexane. This involves drawing a six-membered ring in a staggered conformation, resembling a chair.
3. Place the substituents on the chair conformation. For the cis isomer, both substituents should be on the same side of the ring (either both axial or both equatorial). For the trans isomer, one substituent should be axial and the other equatorial.
4. Draw the second chair conformation by flipping the first chair. This involves converting axial positions to equatorial and vice versa. Ensure that the relative positions (cis or trans) of the substituents are maintained.
5. Determine the more stable conformation by evaluating steric hindrance. Generally, the conformation with the larger substituents in the equatorial position is more stable due to reduced steric strain.

Key Concepts

Chair Conformation

Chair conformation is a three-dimensional shape that cyclohexane adopts to minimize steric strain and torsional strain, making it the most stable conformation. It resembles a chair, with alternating axial and equatorial positions for substituents, which affects the stability of the molecule based on steric interactions.

Axial and Equatorial Positions

In cyclohexane's chair conformation, substituents can occupy axial positions, which are perpendicular to the ring, or equatorial positions, which are parallel to the ring. Equatorial positions are generally more stable due to reduced steric hindrance, especially for larger substituents, influencing the overall stability of the conformation.

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, while in trans isomers, they are on opposite sides. This spatial arrangement affects the stability and energy of the chair conformations, as steric interactions differ between the two isomers.