Chapter 6, Problem 67P

(a)

Interpretation Introduction

Interpretation:

The alkene and reagents used for the preparation of given compounds should be determined.

Concept Introduction:

$H_2$addition:

Catalytic hydrogenation in presence of $\text{Pd/C}$ is an example for syn addition of hydrogen.

For cyclic reactants, the addition of $H_2$ will form cis enantiomers since two hydrogens adds to one side of the double bond.

(b)

Interpretation Introduction

Interpretation:

The alkene and reagents used for the preparation of given compounds should be determined.

Concept Introduction:

Acid Catalysed addition of water: When water is added to alkene in the presence of an acid, the product formed will be an alcohol.

The electrophile ${\text{H}}^{\text{+}}$ adds to the nucleophile alkene and a carbocation is formed. Then water adds to the carbocation and form a protonated alcohol and in the last step it loses a proton and final an alcohol is formed.

(c)

Interpretation Introduction

Interpretation:

The alkene and reagents used for the preparation of given compounds should be determined.

Concept Introduction:

Hydroboration oxidation:

• Used to convert an alkene to alcohol.
• Reagent used is ${\text{BH}}_{\text{3}}\text{or}{\text{R}}_{\text{2}}\text{BH}$
• Boron is the electrophile which accepts electrons from the alkene and forms bond with one ${\text{sp}}^{\text{2}}$ carbon and give ${\text{H}}^{\text{-}}$ to other ${\text{sp}}^{\text{2}}$ carbon.
• After the addition reaction, an aqueous solution of $\text{NaOH}\text{and}{\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$ is added and $\text{OH}$ will be in boron’s place.

(d)

Interpretation Introduction

Interpretation:

The alkene and reagents used for the preparation of given compounds should be determined.

Concept Introduction:

Halogen addition to an alkene:

The addition reaction of halides to alkenes leads to the formation of vicinal dihalide as the product. The two halogens will be on the adjacent carbons.

Mainly ${\text{Br}}_{\text{2}}\text{and}{\text{Cl}}_{\text{2}}$ undergo addition reaction with alkenes and the reaction is carried out in an inert solvent such as dichloromethane.

In general, the reaction can be shown as below.

When the bromine approaches the alkene, one bromine accepts the electrons from alkene and give them to the other bromine and a cyclic bromonium ion intermediate is formed.

The formed unstable intermediate reacts with ${\text{Br}}^{\text{-}}$ and the product is formed.

(e)

Interpretation Introduction

Interpretation:

The alkene and reagents used for the preparation of given compounds should be determined.

Concept Introduction:

Acid Catalysed addition of water: When water is added to alkene in the presence of an acid, the product formed will be an alcohol.

The electrophile ${\text{H}}^{\text{+}}$ adds to the nucleophile alkene and a carbocation is formed. Then water adds to the carbocation and form a protonated alcohol and in the last step it loses a proton and final an alcohol is formed.

(f)

Interpretation Introduction

Interpretation:

The alkene and reagents used for the preparation of given compounds should be determined.

Concept Introduction:

Halogen addition to an alkene:

The addition reaction of halides to alkenes leads to the formation of vicinal dihalide as the product. The two halogens will be on the adjacent carbons.

Mainly ${\text{Br}}_{\text{2}}\text{and}{\text{Cl}}_{\text{2}}$ undergo addition reaction with alkenes and the reaction is carried out in an inert solvent such as dichloromethane.

In general, the reaction can be shown as below.

When the nucleophiles other than water is used, the concentration of the added nucleophile will be greater than the concentration of the halide ion generated from ${\text{Br}}_{\text{2}}\text{or}{\text{Cl}}_{\text{2}}$. If nucleophile like $\text{NaCl}$ is added, ${\text{Na}}^{\text{+}}$ will not take part in reaction and only ${\text{Cl}}^{\text{-}}$ take part in the reaction.