Chapter 3, Problem 3.33SP

(a)

Interpretation Introduction

To determine: The structure and name of any eight isomers among the eighteen isomers of alkane ${\text{C}}_8{\text{H}}_{18}$.

Interpretation: The structure and name of any eight isomers among the eighteen isomers of alkane ${\text{C}}_8{\text{H}}_{18}$ is to be stated.

Concept introduction: The rules for the naming of cycloalkanes are stated below.

• If two different cycloalkanes are present then the one with the more number of carbon atoms act as the parent chain.
• If the side chain has more number of carbon atoms then it act as the parent chain and the cyclic group becomes the substituent and is ended with the word”-yl”.
• The numbering is done in such a manner that the substituents groups occupy the lowest position.
• If different types of substituent groups are present then they are written in an alphabetical order.
• If a substituent is present more than one time then prefixes like di, tri, tetra are used depending on the number of times that particular substituent group appears in the given compound.
• If geometrical isomerism is possible in the given compound then cis and trans is used before the name of the compound.

Answer to Problem 3.33SP

The structure and name of any eight isomers among the eighteen isomers of alkane ${\text{C}}_8{\text{H}}_{18}$ is as follows.

Explanation of Solution

The isomers of given alkane ${\text{C}}_8{\text{H}}_{18}$ are shown below.

Figure 1

The randomly selected first isomer is shown below.

Figure 2

The name of the above compound is octane.

The randomly selected second isomer is shown below.

Figure 3

The name of the above compound is $3-\text{methylheptane}$.

The randomly selected third isomer is shown below.

Figure 4

The name of the above compound is $2,2-\text{dimethylhexane}$.

The randomly selected fourth isomer is shown below.

Figure 5

The name of the above compound is $3,3-\text{dimethylhexane}$.

The randomly selected fifth isomer is shown below.

Figure 6

The name of the above compound is $2,2,4-\text{trimethylpentane}$.

The randomly selected sixth isomer is shown below.

Figure 7

The name of the above compound is $3-\text{ethylhexane}$.

The randomly selected seventh isomer is shown below.

Figure 8

The name of the above compound is $3-\text{ethyl}-3-\text{methylpentane}$.

The randomly selected seventh isomer is shown below.

Figure 9

The name of the above compound is $2,2,3,3-\text{tetramethylbutane}$.

(b)

Interpretation Introduction

To determine: The structure and name of six isomeric cyclopentanes having molecular formula ${\text{C}}_7{\text{H}}_{14}$ including constitutional isomers, of which two show geometric (cis-trans) isomer.

Interpretation: The structure and name of six isomeric cyclopentanes having molecular formula ${\text{C}}_7{\text{H}}_{14}$ including constitutional isomers, of which two show geometric (cis-trans) isomer is to be stated.

Concept introduction: The rules for the naming of cycloalkanes are stated below.

• If two different cycloalkanes are present then the one with the more number of carbon atoms act as the parent chain.
• If the side chain has more number of carbon atoms then it act as the parent chain and the cyclic group becomes the substituent and is ended with the word”-yl”.
• The numbering is done in such a manner that the substituents groups occupy the lowest position.
• If different types of substituent groups are present then they are written in an alphabetical order.
• If a substituent is present more than one time then prefixes like di, tri, tetra are used depending on the number of times that particular substituent group appears in the given compound.
• If geometrical isomerism is possible in the given compound then cis and trans is used before the name of the compound.

Answer to Problem 3.33SP

The structure and name of six isomeric cyclopentanes having molecular formula ${\text{C}}_7{\text{H}}_{14}$ including constitutional isomers, of which two show geometric (cis-trans) isomer is as follows.

Explanation of Solution

The isomers of given cyclopentane ${\text{C}}_7{\text{H}}_{14}$ are shown below.

Figure 10

The first isomer is shown below.

Figure 11

According to IUPAC rules numbering is started from the substituted carbon. Therefore, the name of the above compound is $1,1-\text{dimethylcyclopentane}$.

The second isomer is shown below.

Figure 12

According to IUPAC rules numbering is started from the substituted carbon. Therefore, the name of the above compound is $1-\text{ethylcyclopentane}$.

The third isomer is shown below.

Figure 13

According to IUPAC rules numbering is started from the substituted carbon. Numbering is done in such a manner that the substituents occupy the least position. On the basis of priority of groups $R$ and $S$ configuration has been assigned. Therefore, the name of the above compound is $\left(1R,2S\right)-1,2-\dim \text{ethylcyclopentane}$.

The fourth isomer is shown below.

Figure 14

According to IUPAC rules numbering is started from the substituted carbon. Numbering is done in such a manner that the substituents occupy the least position. On the basis of priority of groups $S$ and $S$ configuration has been assigned. Therefore, the name of the above compound is $\left(1S,2S\right)-1,2-\dim \text{ethylcyclopentane}$.

The fifth isomer is shown below.

Figure 15

According to IUPAC rules numbering is started from the substituted carbon. Numbering is done in such a manner that the substituents occupy the least position. On the basis of priority of groups $S$ and $S$ configuration has been assigned. Therefore, the name of the above compound is $\left(1S,3S\right)-1,3-\dim \text{ethylcyclopentane}$.

The sixth isomer is shown below.

Figure 16

According to IUPAC rules numbering is started from the substituted carbon. Numbering is done in such a manner that the substituents occupy the least position. On the basis of priority of groups $R$ and $S$ configuration has been assigned. Therefore, the name of the above compound is $\left(1R,3S\right)-1,3-\dim \text{ethylcyclopentane}$.