EBK ORGANIC CHEMISTRY
EBK ORGANIC CHEMISTRY
6th Edition
ISBN: 8220103151757
Author: LOUDON
Publisher: MAC HIGHER
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Chapter 7, Problem 7.73AP
Interpretation Introduction

(a)

Interpretation:

The one which is larger among methyl or phenyl is to be stated.

Concept introduction:

In a cyclohexane ring, the steric interactions that takes place between an axial substituent located on the carbon atom 1 and the hydrogen atoms located on carbon 3 and 5 is known as 1, 3 diaxial interaction. In the cyclohexane derivatives, each 1, 3-diaxial interaction between the methyl and hydrogen increases the enthalpy of the ring by 3.7kJmol1.

Expert Solution
Check Mark

Answer to Problem 7.73AP

The value of ΔG°Ph-H shows that compound B is less stable than compound A. Therefore, phenyl is larger.

Explanation of Solution

The two conformations of cyclohexane are given below.

EBK ORGANIC CHEMISTRY, Chapter 7, Problem 7.73AP , additional homework tip  1

Figure 1

In the above shown figure, in conformation A, the number of methyl-hydrogen 1,3-diaxial interactions are two and in conformation B, the number of phenyl-hydrogen 1,3-diaxial interactions are two.

The phenyl group is more bulky than the methyl group. So, it will have a destabilizing effect, and therefore, the equilibrium is favored towards conformation A.

The formula to calculate ΔG° for the above reaction is shown below.

ΔG°BΔG°A=[(2×ΔG°Ph-H)(2×ΔG°CH3-H)]kJmol1

The energy for every methyl-hydrogen 1,3-diaxial interaction is 3.7kJmol1.

The ΔG° for the equilibrium between A and B is 4.73kJmol1.

Substitute the values of energy and ΔG° into the above equation.

4.73kJmol1=[(2×ΔG°Ph-H)(2×3.7)]kJmol14.73kJmol1=[(2×ΔG°Ph-H)(7.4)]kJmol1ΔG°Ph-H=(4.73+7.4)kJmol12ΔG°Ph-H=6.065kJmol1

The value of ΔG°Ph-H shows that compound B is less stable than compound A, so, phenyl is larger.

Conclusion

The equilibrium is favored towards compound A, therefore, phenyl is larger.

Interpretation Introduction

(b)

Interpretation:

The value of ΔG° for two equilibriums is to be calculated.

Concept introduction:

In a cyclohexane ring, the steric interactions that takes place between an axial substituent located on the carbon atom 1 and the hydrogen atoms located on carbon 3 and 5 is known as 1, 3 diaxial interaction. In the cyclohexane derivatives, each 1, 3-diaxial interaction between the methyl and hydrogen increases the enthalpy of the ring by 3.7kJmol1.

Expert Solution
Check Mark

Answer to Problem 7.73AP

(1) The value of ΔG° is 12.13kJmol1.

(2) The value of ΔG° is 2.67kJmol1.

Explanation of Solution

(1) The two conformations of cyclohexane are given below.

EBK ORGANIC CHEMISTRY, Chapter 7, Problem 7.73AP , additional homework tip  2

Figure 2

In the above shown figure, in conformation B, the number of phenyl-hydrogen 1,3-diaxial interactions are two. In conformation A, there is no 1,3-diaxial interaction.

The formula to calculate ΔG° for the above reaction is shown below.

ΔG°BΔG°A=[(2×ΔG°Ph-H)0]kJmol1

The value of ΔG°Ph-H is 6.065kJmol1.

Substitute the value of energy into the above equation.

ΔG°BΔG°A=[(2×ΔG°Ph-H)0]kJmol1ΔG°=[(2×6.065)0]kJmol1ΔG°=12.13kJmol1

(2) The two conformations of cyclohexane are given below.

EBK ORGANIC CHEMISTRY, Chapter 7, Problem 7.73AP , additional homework tip  3

Figure 3

In the above shown figure, in conformation D, the number of phenyl-hydrogen 1,3-diaxial interactions are four. In conformation C, there are two phenyl-hydrogen 1,3-diaxial interaction.

The formula to calculate ΔG° for the above reaction is shown below.

ΔG°DΔG°C=[(4×ΔG°CH3-H)(2×ΔG°Ph-H)]kJmol1

The energy for every methyl-hydrogen 1,3-diaxial interaction is 3.7kJmol1.

The value of ΔG°Ph-H is 6.065kJmol1.

Substitute the values of energy into the above equation.

ΔG°DΔG°C=[(4×3.7)(2×6.065)]kJmol1ΔG°=(14.812.13)kJmol1=2.67kJmol1

Conclusion

The value of ΔG° is 2.67kJmol1.

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Chapter 7 Solutions

EBK ORGANIC CHEMISTRY

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