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Q.35.

Expert-verified
Organic Chemistry
Found in: Page 128

Short Answer

Question: Consider the substituted cyclohexane shown in the ball-and-stick model.

  1. Label the substituents on C1, C2, and C4 as axial or equatorial.
  2. Are the substituents on C1 and C2 cis or trans to each other?
  3. Are the substituents on C2 and C4 cis or trans to each other?
  4. Draw the second possible conformation in the chair form, and classify it as more stable or less stable than the conformation shown in the three-dimensional model.

Answer

a.

b. The substituents at C1 and C2 are cis to each other.

c. The substituents at C2 and C4 are cis to each other.

d.

The most stable chair conformation of substituted cyclohexane

See the step by step solution

Step by Step Solution

Step 1: Conformations of cyclohexane

Cyclohexane exists in the form of chair and boat conformations. The chair conformation of cyclohexane is the most stable form because it can remove the angle strain in the molecule.

The boat conformation is another conformation of cyclohexane. It is the least stable because it has high energy. Cyclohexane occurs in the chair form at room temperature due to high stability.

Step 2: Substituted cyclohexane

The cyclohexane molecule in which the hydrogen atoms are replaced by other groups is substituted cyclohexane.

a. The following is the structure of the given substituted cyclohexane:

Substituted cyclohexane

Carbon 1 consists of one methyl group present at the axial position. Carbon 2 has one bromine atom at the equatorial position. Carbon 4 has one secondary propyl group attached at the equatorial position.

b. Both substituents present at carbon 1 and carbon 2 are cis to each other. They are present on the same side of the molecule.

c. Both substituents present at carbon 2 and carbon 4 are also cis to each other.

Carbon 4 has an isopropyl group and one hydrogen atom. The hydrogen atom is present at the axial position, while the alkyl group occupies the equatorial position. The alkyl group and the bromine atom on carbon 2 are on the same side of the molecule.

d. The second possible chair conformation of the given chair form is shown below:

The most stable chair conformer

The above conformation is obtained by flipping the given structure. The bromine atom has now acquired the axial position at carbon 2. The methyl group is now at the equatorial position.

The substituent at carbon 3, the isopropyl group, is now at the axial position.

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