Chapter 12, Problem 12.36P

Interpretation Introduction

(a)

Interpretation: The given alkenes are to be ranked in order of increasing heats of hydrogenation.

Concept introduction: Hydrogenation reaction is exothermic in nature due to the fact that the bonds are stronger in product than in reactant. Heat of hydrogenation can be used as measure for relative stability of alkenes when they are reduced to same alkane. Higher the stability of alkene, lower is the heat of hydrogenation.

Interpretation Introduction

(b)

Interpretation: The given alkenes are to be ranked in order of increasing rate of reaction with ${\text{H}}_{\text{2}},\text{Pd-C}$.

Concept introduction: The addition of ${\text{H}}_{\text{2}}$ in presence of catalyst is known as catalytic hydrogenation reaction. This is a syn addition. Alkene is reduced to alkane. In this reaction weak pi bond of alkene and sigma bond between ${\text{H}}_{\text{2}}$ is broken and two $\text{C}-\text{H}$ bonds are formed.

Interpretation Introduction

(c)

Interpretation: The products formed when given alkenes are treated with ${\text{O}}_{\text{3}}$ followed by $\text{Zn},{\text{H}}_{\text{2}}\text{O}$ is to be drawn.

Concept introduction: In presence of ozone and $\text{Zn},{\text{H}}_{\text{2}}\text{O}$, oxidative cleavage occurs. In oxidative cleavage both the sigma and pi bond of the alkene is broken and two carbonyl compounds are formed. Depending upon alkyl substituents aldehyde or ketone is formed. When ozone is added to the alkene, unstable intermediate molozonide is formed which rearranges to ozonide. This ozonide is reduced to form two carbonyl compounds in presence of $\text{Zn},{\text{H}}_{\text{2}}\text{O}$.