Chapter 8.18, Problem 43P

a)

Interpretation Introduction

Interpretation:

• The deuterium addition to C-1 rather than to C-4, the reason has to be predicted.

Concept Introduction:

Reactions of conjugated dienes:

An electrophilic addition reaction to a conjugated diene forms both $\text{1,2-addition}$ and $\text{1,4-addition}$ products because the resonance contributors of the allylic cation give cation carbon and the chances for the nucleophile to attack at the electrophilic centre will occur.

Kinetic and thermodynamic products:

Kinetic product: The more rapidly formed product is called the kinetic product.  The reactions that produce the kinetic product as the major product are said to be kinetically controlled.  The kinetic product predominates when the reaction is irreversible.

Thermodynamic product: The more stable product is called the thermodynamic product.  The reactions that produce the thermodynamic product as the major product are said to be thermodynamically controlled.  The thermodynamic product predominates when the reaction is reversible.

Rule: The stabilities of carbocation are,

${\text{Benzyl cation = allyl cation = 3}}^{\circ }{\text{carbocation > 2}}^{\circ }{\text{ carbocation > 1}}^{\circ }\text{ carbocation > methyl cation > vinyl cation}$

b)

Interpretation Introduction

Interpretation:

• The $\text{DCl}$ used rather than $\text{HCl}$, the reason has to be predicted.

Concept Introduction:

Effect of delocalized electrons on the product of the reaction:

The presence of delocalizes electrons while electrophilic addition or substitution the cation intermediate formed is shifted to stable carbocation form at higher rate, and that leads to the product.

Rule: The stabilities of carbocation are,

${\text{Benzyl cation = allyl cation = 3}}^{\circ }{\text{carbocation > 2}}^{\circ }{\text{ carbocation > 1}}^{\circ }\text{ carbocation > methyl cation > vinyl cation}$

Reactions of conjugated dienes:

An electrophilic addition reaction to a conjugated diene forms both $\text{1,2-addition}$ and $\text{1,4-addition}$ products because the resonance contributors of the allylic cation give cation carbon and the chances for the nucleophile to attack at the electrophilic centre will occur.