Chapter 12.5, Problem 12P

Interpretation Introduction

(a)

Interpretation: The product formed when the given compound is treated with ${\text{H}}_{\text{2}}$ (excess), $\text{Pd-C}$ is to be predicted.

Concept introduction: The addition of ${\text{H}}_{\text{2}}$ in presence of catalyst is known as catalytic hydrogenation reaction. This is a syn addition. Alkyne is reduced to alkane. In this reaction, two weak pi bond of alkyne and sigma bond between ${\text{H}}_{\text{2}}$ is broken and four $\text{C}-\text{H}$ bonds are formed.

Interpretation Introduction

(b)

Interpretation: The product formed when the given compound is treated with ${\text{H}}_{\text{2}}$ ($1$ equiv.), Lindlar catalyst is to be predicted.

Concept introduction: The addition of ${\text{H}}_{\text{2}}$ in presence of catalyst is known as catalytic hydrogenation reaction. Lindlar catalyst consists of palladium deposited on calcium carbonate which is poisoned or deactivated by lead or sulfur. In presence of Lindlar catalyst alkyne is reduced to $cis\text{-alkene}$.

Interpretation Introduction

(c)

Interpretation: The product formed when the given compound is treated with ${\text{H}}_{\text{2}}$ (excess), Lindlar catalyst is to be predicted.

Concept introduction: The addition of ${\text{H}}_{\text{2}}$ in presence of catalyst is known as catalytic hydrogenation reaction. Lindlar catalyst consists of palladium deposited on calcium carbonate which is poisoned or deactivated by lead or sulfur. In presence of Lindlar catalyst alkyne is reduced to $cis\text{-alkene}$.

Interpretation Introduction

(d)

Interpretation: The product formed when the given compound is treated with $\text{Na},{\text{NH}}_{\text{3}}$

is to be predicted.

Concept introduction: In presence of sodium metal in ammonia, the is alkyne is reduced to $trans\text{-alkene}$. The addition of ${\text{H}}_{\text{2}}$ takes place in anti fashion to the triple bond. The mechanism involves the addition of electron followed by protonation.