Chapter 8, Problem 99P

(a)

Interpretation Introduction

Interpretation:

• The kinetic and thermodynamic products of the given reaction 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.  The thermodynamic product is the product with the most highly substituted double bond.

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 kinetic and thermodynamic products of the given reaction 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,

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