Question

For trans-1-ethyl-4-isopropylcyclohexane, which two chair conformations are in equilibrium?

Answer 1

Concepts and reason

Chirality center: An atom (usually carbon) which is bonded to four different atoms or groups is known as chiral center.

In the chair conformer, if the atoms are facing towards up, then those atoms must be placed at above the plane in cyclohexane ring structure. Similarly, if the atoms are facing towards down, then those atoms must be placed at below the plane in the cyclohexane ring structure.

Cis isomer contains two groups/substituents on the same side of the ring (either both up or both down). Trans isomer contains two groups/substituents on the opposite side of the ring (one up and one down).

In chair conformation, there is steric interaction developed between the axial groups at first and third positions to each other. This type of interaction is called 1,3-diaxial interaction.

Fundamentals

Cyclohexane is more stable in its chair conformation. In chair conformation of cyclohexane, two types of groups are present at each carbon atom. They are axial and equatorial groups. The six axial bonds one on each carbon, are parallel and alternate up-down.

The six equatorial bonds one on each carbon, come in three sets of two parallel ring bonds. Equatorial bonds alternate between sides around the ring.

The structure is as follows:

The ring flipping is as follows:

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Thus, C and D chair conformations are in equilibrium.

Ans:

The two chair conformations of trans-1-ethyl-4-isopropylcyclohexane are as follows: