From the given isomeric dienes, the compound liberating least heat and the compound liberating most heat upon hydrogenations with 2 moles of hydrogen gases are needed to be identified. Concept introduction: The heat liberation in a reaction is depends upon the stability of the reactant compounds. If the reactant compound is more stable, then the heat liberation will be less. Based on the proximity of C = C bonds in dienes, they are classified into three. Cumulated dienes: the C = C bonds are located adjacent carbons. Conjugated dienes: the C = C bonds or C = C and C = O are separated by one σ-bond. Isolated dienes: the C = C bonds are separated by two or more σ-bonds. The conjugated dienes are more stable as compare to isolated dienes because the delocalization of π bonds is taking place, so this forms some stabilization energy in conjugated system. The more substituted alkenes are more stable as compared to less substituted alkenes . Because the more alkyl group attachment to a double bond make it more stable due to the + I effect of alkyl groups. It means the alkyl groups will push electrons towards the double bonded carbon atoms, so the double bond becomes strengthened and highly stabilized . To identify: the compound liberating least heat and the compound liberating most heat upon hydrogenations with 2 moles of hydrogen gases from the given isomeric dienes.

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Chapter 16.2, Problem 4CC

(a)

Interpretation Introduction

Interpretation:

From the given isomeric dienes, the compound liberating least heat and the compound liberating most heat upon hydrogenations with 2 moles of hydrogen gases are needed to be identified.

Concept introduction:

The heat liberation in a reaction is depends upon the stability of the reactant compounds. If the reactant compound is more stable, then the heat liberation will be less.

Based on the proximity of C = C bonds in dienes, they are classified into three.

Cumulated dienes: the C = C bonds are located adjacent carbons.

Conjugated dienes: the C = C bonds or C = C and C = O are separated by one σ-bond.

Isolated dienes: the C = C bonds are separated by two or more σ-bonds.

The conjugated dienes are more stable as compare to isolated dienes because the delocalization of π bonds is taking place, so this forms some stabilization energy in conjugated system.

The more substituted alkenes are more stable as compared to less substituted alkenes. Because the more alkyl group attachment to a double bond make it more stable due to the ⁺I effect of alkyl groups. It means the alkyl groups will push electrons towards the double bonded carbon atoms, so the double bond becomes strengthened and highly stabilized.

To identify: the compound liberating least heat and the compound liberating most heat upon hydrogenations with 2 moles of hydrogen gases from the given isomeric dienes.

(b)

Interpretation Introduction

Interpretation:

From the given isomeric dienes, the compound liberating least heat and the compound liberating most heat upon hydrogenations with 2 moles of hydrogen gases are needed to be identified.

Concept introduction:

The heat liberation in a reaction is depends upon the stability of the reactant compounds. If the reactant compound is more stable, then the heat liberation will be less.

Based on the proximity of C = C bonds in dienes, they are classified into three.

Cumulated dienes: the C = C bonds are located adjacent carbons.

Conjugated dienes: the C = C bonds or C = C and C = O are separated by one σ-bond.

Isolated dienes: the C = C bonds are separated by two or more σ-bonds.

The conjugated dienes are more stable as compare to isolated dienes because the delocalization of π bonds is taking place, so this forms some stabilization energy in conjugated system.

The more substituted alkenes are more stable as compared to less substituted alkenes. Because the more alkyl group attachment to a double bond make it more stable due to the ⁺I effect of alkyl groups. It means the alkyl groups will push electrons towards the double bonded carbon atoms, so the double bond becomes strengthened and highly stabilized.

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