Chapter 21, Problem 16E

Draw all the structural isomers for C₈H₁₈ that have the following root name (longest carbon chain). Name the structural isomers.

a. hexane

b. pentane

Interpretation Introduction

Interpretation: The structural isomers of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ that have the root name hexane and pentane are to be drawn and their names are to be stated.

Concept introduction: Rules given by IUPAC should be followed to name an organic compound. Any organic compound has only one name that denotes that compound. The root word determines the number of carbons while counting the longest carbon chain. If more than one substituent is present, prefixes like di, tri, tetra, etc. are used and different substituents are written in alphabetical order.

Answer to Problem 16E

Answer

The structural isomers of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ that have the root name pentane are drawn and their names have been rightfully stated.

Explanation of Solution

Explanation

To determine: The structural isomers of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ that have the root name hexane.

The structural isomer is given below and its name is $3$-ethylhexane.

The structure of the isomer is,

Figure 1

The general formula of alkanes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}$. The given formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ satisfy the general formula of alkanes. Eight carbons means the the root word is “octane”. Thus the given formula signifies the organic compound octane.

Octane has eight carbons and $18$ hydrogens. $3$-ethylhexane also have eight carbons and $18$ hydrogens, but its structure is different from octane. Therefore, $3$-ethylhexane is a structural isomer of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$.

The isomer has six carbons in the parent chain. Therefore the root word “hexane” is used. Ethyl group is attached to third carbon, thus the name of the isomer is $3$-ethylhexane.

The structural isomer is given below and its name is $2,2$-dimethylhexane.

The structure of the isomer is,

Figure 2

The general formula of alkanes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}$. The given formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ satisfy the general formula of alkanes. Eight carbons means the the root word is “octane”. Thus the given formula signifies the organic compound octane.

Octane has eight carbons and $18$ hydrogens. $2,2$-dimethylhexane also have eight carbons and $18$ hydrogens, but its structure is different from octane. Therefore, $2,2$-dimethylhexane is a structural isomer of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$.

The isomer has six carbons in the parent chain. Therefore the root word “hexane” is used. Two methyl groups are attached to second carbon, thus the name of the isomer is $2,2$-dimethylhexane.

The structural isomer is given below and its name is $2,3$-dimethylhexane.

The structure of the given isomer is,

Figure 3

The general formula of alkanes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}$. The given formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ satisfy the general formula of alkanes. Eight carbons means the the root word is “octane”. Thus the given formula signifies the organic compound octane.

Octane has eight carbons and $18$ hydrogens. $2,3$-dimethylhexane also have eight carbons and $18$ hydrogens, but its structure is different from octane. Therefore, $2,3$-dimethylhexane is a structural isomer of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$.

The isomer has six carbons in the parent chain. Therefore the root word “hexane” is used. Methyl group is attached to second and third carbon, thus the name of the isomer is $2,3$-dimethylhexane.

The structural isomer is given below and its name is $2,4$-dimethylhexane.

The structure of the isomer is,

Figure 4

The general formula of alkanes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}$. The given formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ satisfy the general formula of alkanes. Eight carbons means the the root word is “octane”. Thus the given formula signifies the organic compound octane.

Octane has eight carbons and $18$ hydrogens. $2,4$-dimethylhexane also have eight carbons and $18$ hydrogens, but its structure is different from octane. Therefore, $2,4$-dimethylhexane is a structural isomer of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$.

The isomer has six carbons in the parent chain. Therefore the root word “hexane” is used. Methyl group is attached to second and fourth carbon, thus the name of the isomer is $2,4$-dimethylhexane.

The structural isomer is given below and its name is $2,5$-dimethylhexane.

The structure of the isomer is,

Figure 5

The general formula of alkanes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}$. The given formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ satisfy the general formula of alkanes. Eight carbons means the the root word is “octane”. Thus the given formula signifies the organic compound octane.

Octane has eight carbons and $18$ hydrogens. $2,5$-dimethylhexane also have eight carbons and $18$ hydrogens, but its structure is different from octane. Therefore, $2,5$-dimethylhexane is a structural isomer of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$.

The isomer has six carbons in the parent chain. Therefore the root word “hexane” is used. Methyl group is attached to second and fifth carbon, thus the name of the isomer is $2,5$-dimethylhexane.

The structural isomer is given below and its name is $3,3$-dimethylhexane.

The structure of the isomer is,

Figure 6

The general formula of alkanes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}$. The given formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ satisfy the general formula of alkanes. Eight carbons means the the root word is “octane”. Thus the given formula signifies the organic compound octane.

Octane has eight carbons and $18$ hydrogens. $3,3$-dimethylhexane also have eight carbons and $18$ hydrogens, but its structure is different from octane. Therefore, $3,3$-dimethylhexane is a structural isomer of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$.

The isomer has six carbons in the parent chain. Therefore the root word “hexane” is used. Two Methyl groups are attached to third carbon, thus the name of the isomer is $3,3$-dimethylhexane.

The structural isomer is given below and its name is $3,4$-dimethylhexane.

The structure of the isomer is,

Figure 7

The general formula of alkanes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}$. The given formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ satisfy the general formula of alkanes. Eight carbons means the the root word is “octane”. Thus the given formula signifies the organic compound octane.

Octane has eight carbons and $18$ hydrogens. $3,4$-dimethylhexane also have eight carbons and $18$ hydrogens, but its structure is different from octane. Therefore, $3,4$-dimethylhexane is a structural isomer of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$.

The isomer has six carbons in the parent chain. Therefore the root word “hexane” is used. Methyl groups are attached to third and fourth carbon, thus the name of the isomer is $3,4$-dimethylhexane.

Conclusion

Conclusion

The structural isomers of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ that have the root name hexane are drawn and their names have been rightfully stated.

Interpretation Introduction

Interpretation: The structural isomers of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ that have the root name hexane and pentane are to be drawn and their names are to be stated.

Concept introduction: Rules given by IUPAC should be followed to name an organic compound. Any organic compound has only one name that denotes that compound. The root word determines the number of carbons while counting the longest carbon chain. If more than one substituent is present, prefixes like di, tri, tetra, etc. are used and different substituents are written in alphabetical order.

Explanation of Solution

Explanation

To determine: The structural isomers of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ that have the root name pentane.

The structural isomer is given below and its name is $3$-ethyl- $2$-methylpentane.

The structure of the isomer is,

Figure 8

The general formula of alkanes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}$. The given formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ satisfy the general formula of alkanes. Eight carbons means the the root word is “octane”. Thus the given formula signifies the organic compound octane.

Octane has eight carbons and $18$ hydrogens. $3$-ethyl- $2$-methylpentane also have eight carbons and $18$ hydrogens, but its structure is different from octane. Therefore, $3$-ethyl- $2$-methylpentane is a structural isomer of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$.

The isomer has five carbons in the parent chain. Therefore the root word “pentane” is used. Methyl group is attached to second carbon, ethyl group is attached to third carbon, therefore, the name of the isomer is $3$-ethyl- $2$-methylpentane.

The structural isomer is given below and its name is $3$-ethyl- $3$-methylpentane.

The structure of the isomer is,

Figure 9

The general formula of alkanes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}$. The given formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ satisfy the general formula of alkanes. Eight carbons means the the root word is “octane”. Thus the given formula signifies the organic compound octane.

Octane has eight carbons and $18$ hydrogens. $3$-ethyl- $3$-methylpentane also have eight carbons and $18$ hydrogens, but its structure is different from octane. Therefore, $3$-ethyl- $3$-methylpentane is a structural isomer of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$.

The isomer has five carbons in the parent chain. Therefore the root word “pentane” is used. Methyl group and ethyl group is attached to third carbon, therefore, the name of the isomer is $3$-ethyl- $3$-methylpentane.

The structural isomer is given below and its name is $2,2,3$-trimethylpentane.

The structure of the isomer is,

Figure 10

The general formula of alkanes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}$. The given formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ satisfy the general formula of alkanes. Eight carbons means the the root word is “octane”. Thus the given formula signifies the organic compound octane.

Octane has eight carbons and $18$ hydrogens. $2,2,3$-trimethylpentane also have eight carbons and $18$ hydrogens, but its structure is different from octane. Therefore, $2,2,3$-trimethylpentane is a structural isomer of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$.

The isomer has five carbons in the parent chain. Therefore the root word “pentane” is used. Two methyl groups are attached to second carbon and one methyl group is attached to third carbon, therefore, the name of the isomer is $2,2,3$-trimethylpentane.

The structural isomer is given below and its name is $2,2,4$-trimethylpentane.

The structure of the isomer is,

Figure 11

The general formula of alkanes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}$. The given formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ satisfy the general formula of alkanes. Eight carbons means the the root word is “octane”. Thus the given formula signifies the organic compound octane.

Octane has eight carbons and $18$ hydrogens. $2,2,4$-trimethylpentane also have eight carbons and $18$ hydrogens, but its structure is different from octane. Therefore, $2,2,4$-trimethylpentane is a structural isomer of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$.

The isomer has five carbons in the parent chain. Therefore the root word “pentane” is used. Two methyl groups are attached to second carbon and one methyl group is attached to fourth carbon, therefore, the name of the isomer is $2,2,4$-trimethylpentane.

The structural isomer is given below and its name is $2,3,3$-trimethylpentane.

The structure of the isomer is,

Figure 12

The general formula of alkanes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}$. The given formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ satisfy the general formula of alkanes. Eight carbons means the the root word is “octane”. Thus the given formula signifies the organic compound octane.

Octane has eight carbons and $18$ hydrogens. $2,3,3$-trimethylpentane also have eight carbons and $18$ hydrogens, but its structure is different from octane. Therefore, $2,3,3$-trimethylpentane is a structural isomer of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$.

The isomer has five carbons in the parent chain. Therefore the root word “pentane” is used. Two methyl groups are attached to third carbon and one methyl group is attached to second carbon, therefore, the name of the isomer is $2,3,3$-trimethylpentane.

The structural isomer is given below and its name is $2,3,4$-trimethylpentane.

The structure of the isomer is,

Figure 13

The general formula of alkanes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}$. The given formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ satisfy the general formula of alkanes. Eight carbons means the the root word is “octane”. Thus the given formula signifies the organic compound octane.

Octane has eight carbons and $18$ hydrogens. $2,3,4$-trimethylpentane also have eight carbons and $18$ hydrogens, but its structure is different from octane. Therefore, $2,3,4$-trimethylpentane is a structural isomer of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$.

The isomer has five carbons in the parent chain. Therefore the root word “pentane” is used. Methyl group is attached to second, third carbon and fourth carbon, therefore, the name of the isomer is $2,3,4$-trimethylpentane.

Conclusion

Conclusion

The structural isomers of ${\text{C}}_{\text{8}}{\text{H}}_{\text{18}}$ that have the root name pentane are drawn and their names have been rightfully stated.