Organic Chemistry
Organic Chemistry
6th Edition
ISBN: 9781936221349
Author: Marc Loudon, Jim Parise
Publisher: W. H. Freeman
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Chapter 7, Problem 7.14P
Interpretation Introduction

(a)

Interpretation:

The energy difference between the two chair conformations of trans1,4dimethylcylohexane is to be calculated.

Concept introduction:

The conformation of cyclohexane is a type of 3D shape of cyclohexane molecule. There are total four types of significant conformations of cyclohexane exists which are chair conformation, half-chair conformation, boat conformation and twist-boat conformation. The switching of cyclohexane molecule is very easy between the four conformations.

Expert Solution
Check Mark

Answer to Problem 7.14P

The energy difference between the two chair conformations of trans1,4dimethylcylohexane is 14.8kJmol1.

Explanation of Solution

The two chair conformations of trans1,4dimethylcylohexane are shown below.

Organic Chemistry, Chapter 7, Problem 7.14P , additional homework tip  1

Figure 1

The 1,3diaxial interaction between hydrogen and methyl present in the chair conformation A of trans1,4dimethylcylohexane that is shown as,

Organic Chemistry, Chapter 7, Problem 7.14P , additional homework tip  2

Figure 2

Thus, there are total four 1,3diaxial interactions between hydrogen and methyl present in the given compound.

The given value of contribution one 1,3diaxial interaction between hydrogen and methyl in energy is 3.7kJmol1(0.9kcal/mol). Therefore, the contribution of four 1,3diaxial interactions in energy is calculated as,

Energycontributedbyfour 1,3diaxialinteraction=4×3.7kJmol1=14.8kJmol1

In case of chair conformation B, there is no 1,3diaxial interaction exists between hydrogen and methyl. Thus, its energy contribution is zero.

Therefore, the energy difference of between the two chair conformations of trans1,4dimethylcylohexane is calculated as,

Energydifference=EnergygivenbyconformationAEnergygivenbyconformationB

Substitute the values of energies in above equation.

Energydifference=14.8kJmol10kJmol1=14.8kJmol1

Thus, the energy difference is 14.8kJmol1.

Conclusion

The energy difference between the two chair conformations of the given compound is 14.8kJmol1.

Interpretation Introduction

(b)

Interpretation:

The energy difference between cis1,4dimethylcylohexane and the more stable conformation of trans1,4dimethylcylohexane is to be calculated.

Concept introduction:

The conformation of cyclohexane is a type of 3D shape of cyclohexane molecule. There are total four types of significant conformations of cyclohexane exists which are chair conformation, half-chair conformation, boat conformation and twist-boat conformation. The switching of cyclohexane molecule is very easy between the four conformations.

Expert Solution
Check Mark

Answer to Problem 7.14P

The energy difference between cis1,4dimethylcylohexane and the more stable conformation of trans1,4dimethylcylohexane is 7.4kJmol1.

Explanation of Solution

The chair conformations of cis1,4dimethylcylohexane are shown below.

Organic Chemistry, Chapter 7, Problem 7.14P , additional homework tip  3

Figure 3

The 1,3diaxial interaction between hydrogen and methyl present in the chair conformation of cis1,4dimethylcylohexane that is shown as,

Organic Chemistry, Chapter 7, Problem 7.14P , additional homework tip  4

Figure 4

The given value of contribution one 1,3diaxial interaction between hydrogen and methyl in energy is 3.7kJmol1(0.9kcal/mol). Therefore, the contribution of two 1,3diaxial interactions in energy is calculated as,

Energycontributedbytwo 1,3diaxialinteraction=2×3.7kJmol1=7.4kJmol1

The most stable chair conformation of trans1,4dimethylcylohexane are shown below.

Organic Chemistry, Chapter 7, Problem 7.14P , additional homework tip  5

Figure 5

In case of most stable chair conformation of trans1,4dimethylcylohexane, there is no 1,3diaxial interaction exists between hydrogen and methyl. Thus, its energy contribution is zero.

Therefore, the energy difference of between the two chair conformations of trans1,4dimethylcylohexane and cis1,4dimethylcylohexane is calculated as,

Energydifference=EnergygivenbyconformationAEnergygivenbyconformationB

Substitute the values of energies in above equation.

Energydifference=7.4kJmol10kJmol1=7.4kJmol1

Thus, the energy difference is 7.4kJmol1.

Conclusion

The energy difference between cis1,4dimethylcylohexane and the more stable conformation of trans1,4dimethylcylohexane is 7.4kJmol1.

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