Question

A trisubstituted cyclohexane compound is given below in its chair conformation. Draw the corresponding planar (overhead) representation, using wedges and hashed bonds to indicate the substituent positions. To be graded properly, include the hydrogen atoms on the chirality centers (asymmetric carbons). Be sure that both wedges/hashed bonds are drawn on the outside of the ring, or else the stereochemistry may be interpreted as square planar.

Answer 1

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

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

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.

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.

The structure is as follows:

In this structure, the -Cl group is pointed towards up, -F and -Br groups are pointed towards down.

Number the chair conformer and see that the substituents get the lowest possible number.

Number the ring as follows:

‎

In this structure, the -Br group is at 1^st carbon atom, -F group is at 2^nd carbon atom and the -Cl group is at 3^rd carbon atom.

Make sure that the substituents get the lowest number on the cyclic ring.

Add the substituents present on the chair form to the cyclohexane ring structure.

The substituents are placed in cyclohexane ring as follows:

Thus, the trisubstituted cyclohexane structure is as follows:

The -Br group is placed below the plane in cyclohexane ring, as it is facing towards down in chair conformer. So, the hydrogen atom is placed below the plane.

The -F group is placed below the plane in cyclohexane ring, as it is facing towards down in chair conformer. So, the hydrogen atom is placed below the plane.

The -Cl group is placed above the plane in cyclohexane ring, as it is facing towards up in chair conformer. So, the hydrogen atom is placed above the plane.

Answer 2

Trisubstitutef