Chapter 7, Problem 7.55AP

Interpretation Introduction

(a)

Interpretation:

The structure and the stereochemistry of products formed by the reaction, $trans\text{-2-pentene}+{\text{Br}}_{\text{2}}\to$, is to be stated. Whether the stereo isomeric products that are formed are in the same or different amounts, are 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 bonds of alkyne and sigma bond between ${\text{H}}_{\text{2}}$ is broken and four $\text{C}-\text{H}$ bonds are formed.

Answer to Problem 7.55AP

The products formed by the reaction, $trans\text{-2-pentene}+{\text{Br}}_{\text{2}}\to$, is $\text{2, 3-dibromopentane}$. The structure of the product formed is shown below.

The stereo isomeric products that are formed are in the same amounts. Therefore, the racemic mixture is obtained.

Explanation of Solution

The reaction of $trans\text{-2-pentene}$ with ${\text{Br}}_{\text{2}}$ gives $\text{2, 3-dibromopentane}$. The addition occurs in the anti-manner. The corresponding reaction is shown below.

Figure 1

The products obtained are in equal ratio. Therefore, the racemic mixture is obtained.

Conclusion

The products formed by the reaction $trans\text{-2-pentene}+{\text{Br}}_{\text{2}}\to$, is $\text{2, 3-dibromopentane}$. The structure is shown in Figure 1. The stereo isomeric products that are formed are in the same amounts.

Interpretation Introduction

(b)

Interpretation:

The structure and the stereochemistry of products formed by the reaction, $trans\text{-3-hexene}+{\text{Br}}_{\text{2}}+\underset{\begin{array}{l}\text{excess}\\ \left(\text{solvent}\right)\end{array}}{{\text{H}}_{\text{2}}\text{O}}\to$, is to be stated. Whether the stereo isomeric products that are formed are in the same or different amounts, are 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 bonds of alkyne and sigma bond between ${\text{H}}_{\text{2}}$ is broken and four $\text{C}-\text{H}$ bonds are formed.

Answer to Problem 7.55AP

The products formed by the reaction $trans\text{-3-hexene}+{\text{Br}}_{\text{2}}+\underset{\begin{array}{l}\text{excess}\\ \left(\text{solvent}\right)\end{array}}{{\text{H}}_{\text{2}}\text{O}}\to$, is $\text{3-bromohex-4-ol}$. The structure is shown below.

The stereo isomeric products that are formed are in the same amounts. Therefore, the racemic mixture is obtained.

Explanation of Solution

The reaction of $trans\text{-3-hexene}$ with ${\text{Br}}_{\text{2}}/{\text{H}}_{\text{2}}\text{O}$ gives $\text{3-bromohex-4-ol}$. The addition occurs in the anti-manner. The corresponding reaction is shown below.

Figure 2

The products obtained are in equal ratio. Therefore, the racemic mixture is obtained.

Conclusion

The products formed by the reaction $trans\text{-3-hexene}+{\text{Br}}_{\text{2}}+\underset{\begin{array}{l}\text{excess}\\ \left(\text{solvent}\right)\end{array}}{{\text{H}}_{\text{2}}\text{O}}\to$, is $\text{3-bromohex-4-ol}$. The structure is shown in Figure 2. The stereo isomeric products that are formed are in the same amounts.

Interpretation Introduction

(c)

Interpretation:

The structure and the stereochemistry of products formed by the reaction $cis\text{-3-hexene}+{\text{D}}_2\stackrel{\text{Pt}/\text{C}}{\to }$, is to be stated. Whether the stereo isomeric products that are formed are in the same or different amounts, are 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 bonds of alkyne and sigma bond between ${\text{H}}_{\text{2}}$ is broken and four $\text{C}-\text{H}$ bonds are formed.

Answer to Problem 7.55AP

The products formed by the reaction $cis\text{-3-hexene}+{\text{D}}_2\stackrel{\text{Pt}/\text{C}}{\to }$, is deuterated hexane. The structure is shown below.

The stereoisomeric product that is obtained by the $cis\text{-3-hexene}+{\text{D}}_2\stackrel{\text{Pt}/\text{C}}{\to }$ reaction is meso compound.

Explanation of Solution

The reaction of $cis\text{-3-hexene}$ with ${\text{D}}_2$ gives deuterated hexane. The addition occurs in the syn-manner. The corresponding reaction is shown below.

Figure 3

Therefore, the compound obtained is meso compound.

Conclusion

The products formed by the reaction $cis\text{-3-hexene}+{\text{D}}_2\stackrel{\text{Pt}/\text{C}}{\to }$, is deuterated hexane. The structure is shown in Figure 3.

The stereo isomeric product that is obtained by the $cis\text{-3-hexene}+{\text{D}}_2\stackrel{\text{Pt}/\text{C}}{\to }$ reaction is meso compound.

Interpretation Introduction

(d)

Interpretation:

The structure and the stereochemistry of products formed by the reaction $cis\text{-3-hexene}+{\text{BD}}_{\text{3}}\underset{\text{THF}}{\to }\stackrel{{\text{H}}_2{\text{O}}_2/{}^{-}\text{OH}}{\to }$, is to be stated. Whether the stereo isomeric products that are formed are in the same or different amounts, are 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 bonds of alkyne and sigma bond between ${\text{H}}_{\text{2}}$ is broken and four $\text{C}-\text{H}$ bonds are formed.

Answer to Problem 7.55AP

The product formed by the reaction, $cis\text{-3-hexene}+{\text{BD}}_{\text{3}}\underset{\text{THF}}{\to }\stackrel{{\text{H}}_2{\text{O}}_2/{}^{-}\text{OH}}{\to }$, is deuterated alcohol. The structure of the alcohol is shown below.

The stereo isomeric products that are formed are in the same amounts. Therefore, the racemic mixture is obtained.

Explanation of Solution

The reaction of $cis\text{-3-hexene}$ with ${\text{BD}}_{\text{3}}$ followed by the oxidation with ${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}/\text{O}\text{H}$ gives deuterated alcohol. The addition occurs in the syn-manner. The corresponding reaction is shown below.

Figure 4

The products obtained are in equal ratio. Therefore, the racemic mixture is obtained.

Conclusion

The products formed by the reaction $cis\text{-3-hexene}+{\text{BD}}_{\text{3}}\underset{\text{THF}}{\to }\stackrel{{\text{H}}_2{\text{O}}_2/{}^{-}\text{OH}}{\to }$, is deuterated alcohol. The structure of the alcohol is shown in Figure 4.

The stereo isomeric products that are formed are in the same amounts.