Chapter 7.8, Problem 17P

(a)

Interpretation Introduction

Interpretation:

The products obtained from the acid catalysed addition of water and hydroboration reaction of the given compound should be determined.

Concept Introduction:

Hydroboration-oxidation reaction:

• Internal alkynes oxidize to form ketones.
• Terminal alkyne oxidize to form aldehyde.
• Reagents used are ${\text{BH}}_{\text{3}}\text{and}{\text{R}}_{\text{2}}\text{BH}$ for internal alkyne.
• ${\text{R}}_{\text{2}}\text{BH}$ is the reagent used for terminal alkynes.

General mechanism for hydroboration oxidation:

Acid Catalysed addition of water: When water is added to alkyne in the presence of an acid, the product formed will be an enol.  Enol contains a double bond and an $\text{OH}$ group.  The $\text{OH}$ group is bonded to one of the ${\text{sp}}^{\text{2}}$ carbons.

If a carbonyl group is bonded to two alkyl groups, it is called as a ketone.  The enol formed in the acid catalysed addition of water will be easily converted into an ketone.

Conversion of terminal alkynes into enol: If we want to convert terminal alkyne into an enol, the presence of mercuric ion as a catalyst should be needed and the catalyst will increase the rate of the reaction.

(b)

Interpretation Introduction

Interpretation:

The products obtained from the acid catalysed addition of water and hydroboration reaction of the given compound should be determined.

Concept Introduction:

Hydroboration-oxidation reaction:

• Internal alkynes oxidize to form ketones.
• Terminal alkyne oxidize to form aldehyde.
• Reagents used are ${\text{BH}}_{\text{3}}\text{and}{\text{R}}_{\text{2}}\text{BH}$ for internal alkyne.
• ${\text{R}}_{\text{2}}\text{BH}$ is the reagent used for terminal alkynes.

General mechanism for hydroboration oxidation:

Acid Catalysed addition of water: When water is added to alkyne in the presence of an acid, the product formed will be an enol.  Enol contains a double bond and an $\text{OH}$ group. The $\text{OH}$ group is bonded to one of the ${\text{sp}}^{\text{2}}$ carbons.

If a carbonyl group is bonded to two alkyl groups, it is called as a ketone.  The enol formed in the acid catalysed addition of water will be easily converted into an ketone.

Conversion of terminal alkynes into enol: If we want to convert terminal alkyne into an enol, the presence of mercuric ion as a catalyst should be needed and the catalyst will increase the rate of the reaction.

(c)

Interpretation Introduction

Interpretation:

The products obtained from the acid catalysed addition of water and hydroboration reaction of the given compounds should be determined.

Concept Introduction:

Hydroboration-oxidation reaction:

• Internal alkynes oxidize to form ketones.
• Terminal alkyne oxidize to form aldehyde.
• Reagents used are ${\text{BH}}_{\text{3}}\text{and}{\text{R}}_{\text{2}}\text{BH}$ for internal alkyne.
• ${\text{R}}_{\text{2}}\text{BH}$ is the reagent used for terminal alkynes.

General mechanism for hydroboration oxidation:

Acid Catalysed addition of water: When water is added to alkyne in the presence of an acid, the product formed will be an enol.  Enol contains a double bond and an $\text{OH}$ group. The $\text{OH}$ group is bonded to one of the ${\text{sp}}^{\text{2}}$ carbons.

If a carbonyl group is bonded to two alkyl groups, it is called as a ketone.  The enol formed in the acid catalysed addition of water will be easily converted into an ketone.

Conversion of terminal alkynes into enol: If we want to convert terminal alkyne into an enol, the presence of mercuric ion as a catalyst should be needed and the catalyst will increase the rate of the reaction.