Chair Conformation: Maximizing Stability with Substituents

How can we determine the most stable chair conformation of cyclohexane compounds?

a. trans-1-isopropyl-3-methylcyclohexane

b. cis-1-sec-butyl-4-ethylcyclohexane

c. cis-1-ethyl-2-isobutylcyclohexane

d. trans-1,2-dibutylcyclohexane

Explanation:

In determining the most stable chair conformation of cyclohexane compounds, we need to consider the concept of steric hindrance. Steric hindrance is the repulsion that occurs between atoms that are too close together, leading to instability in the molecule.

When analyzing the different chair conformations provided:

a. trans-1-isopropyl-3-methylcyclohexane: The isopropyl group and the methyl group are both in equatorial positions, pointing away from the ring, and experience the least steric hindrance, making this conformation the most stable.

b. cis-1-sec-butyl-4-ethylcyclohexane: The sec-butyl group and the ethyl group are both in axial positions, pointing towards the ring, and experience the most steric hindrance, making this conformation the least stable.

c. cis-1-ethyl-2-isobutylcyclohexane: The ethyl group and the isobutyl group are both in axial positions, pointing towards the ring, and experience high steric hindrance, making this conformation less stable compared to others.

d. trans-1,2-dibutylcyclohexane: The butyl groups are both in equatorial positions, pointing away from the ring, and experience the least steric hindrance, making this conformation relatively stable.

In conclusion, the positioning of substituents in chair conformations plays a crucial role in determining the stability of the molecule based on steric hindrance.