Q.4-24E - Organic Chemistry (Mcmurry)

Question

A trisubstituted cyclohexane with three substituents—red, green, and blue—undergoes a ring-flip to its alternate chair conformation. Identify each substituent as axial or equatorial, and show the positions occupied by the three substituents in the ring-flipped form.

Step-by-Step Solution

Answer

The Methyl group is present at the axial position, and chlorine is present at the equatorial position. Given structure is less stable chair conformation.

Definition of Chair confirmation

Chair conformation structure for the six-membered ring is when atoms 2, 3, 5, and 6 lie in the same plane, atom 1 lies above the plane, and atom 4 lies below the plane.

Definition of Axial and equatorial positions

Axial bonds are the bonds that are perpendicular or vertical to the ring plane. Equatorial bonds are approximately horizontal in the plane of the ring. 

Ring flip

Ring-flip in chair cyclohexane interconverts axial and equatorial positions. The axial atoms in the starting structure become equatorial in the ring-flipped structure and vice-versa.

Positions before ring flip

Here green and red are present vertically in the ring, indicating it is at the axial position. Blue is present approximately horizontal in the plane of the ring, indicating its equatorial position.

Positions after ring flip

Here, blue is present vertical to the ring, at the axial position, and red and green are present approximately horizontal in the plane of the ring, at the equatorial position after the ring flip.