Chapter 7.9, Problem 20P

(a)

Interpretation Introduction

Interpretation:

The product formed in the given reaction should be determined.

Concept Introduction:

Deprotonation: The reaction in which proton is removed from the compound using reagents is known as deprotonation.

Different reagents are used for the deprotonation and one of the common reagent is sodium amide.

${\text{NaNH}}_{\text{2}}$ will deprotonate alkynes, alcohols and as a strong base it will deprotonate alkynes and produces acetylide ion.

Lindlar catalyst: The catalyst is used for the hydrogenation of alkynes in a syn manner.  This means both hydrogen are added on the same side across the triple bond and the product obtained will be a cis product.

Sodium in liquid ammonia: The catalyst is used for the formation of trans alkenes from alkynes. Because of its more reactivity towards triple bonds, the reaction will stop at the formation of alkenes.

$Pd/C$: Hydrogenation can done using this catalyst and converts alkenes to alkanes. The addition will be a syn addition.

(b)

Interpretation Introduction

Interpretation:

The product formed in the given reaction should be determined.

Concept Introduction:

Deprotonation: The reaction in which proton is removed from the compound using reagents is known as deprotonation.

Different reagents are used for the deprotonation and one of the common reagent is sodium amide.

${\text{NaNH}}_{\text{2}}$ will deprotonate alkynes, alcohols and as a strong base it will deprotonate alkynes and produces acetylide ion.

Lindlar catalyst: The catalyst is used for the hydrogenation of alkynes in a syn manner.  This means both hydrogen are added on the same side across the triple bond and the product obtained will be a cis product.

Sodium in liquid ammonia: The catalyst is used for the formation of trans alkenes from alkynes. Because of its more reactivity towards triple bonds, the reaction will stop at the formation of alkenes.

$Pd/C$: Hydrogenation can done using this catalyst and converts alkenes to alkanes. The addition will be a syn addition.

(c)

Interpretation Introduction

Interpretation:

The product formed in the given reaction should be determined.

Concept Introduction:

Deprotonation: The reaction in which proton is removed from the compound using reagents is known as deprotonation.

Different reagents are used for the deprotonation and one of the common reagent is sodium amide.

${\text{NaNH}}_{\text{2}}$ will deprotonate alkynes, alcohols and as a strong base it will deprotonate alkynes and produces acetylide ion.

Lindlar catalyst: The catalyst is used for the hydrogenation of alkynes in a syn manner.  This means both hydrogen are added on the same side across the triple bond and the product obtained will be a cis product.

Sodium in liquid ammonia: The catalyst is used for the formation of trans alkenes from alkynes. Because of its more reactivity towards triple bonds, the reaction will stop at the formation of alkenes.

$Pd/C$: Hydrogenation can done using this catalyst and converts alkenes to alkanes. The addition will be a syn addition.

(d)

Interpretation Introduction

Interpretation:

The product formed in the given reaction 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:

(e)

Interpretation Introduction

Interpretation:

The product formed in the given reaction 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:

(f)

Interpretation Introduction

Interpretation:

The products formed in the given reaction should be determined.

Concept Introduction:

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.