Identifying Isomers Write structural formulas for all the constitutional isomers with the molecular formula C5H12. Analyze First we write the longest chain of C atoms and add an appropriate number of H atoms (12, in this case) to give each C atom four bonds. Next, we look for isomers that have

Question

Identifying Isomers

Write structural formulas for all the constitutional isomers with the molecular formula [latex]C_5H_{12}[/latex].

Analyze
First we write the longest chain of C atoms and add an appropriate number of H atoms (12, in this case) to give each C atom four bonds. Next, we look for isomers that have fewer carbon atoms in the longest chain.

Accepted Answer

The longest chain of carbon atoms that we can draw has five carbon atoms in it. When we add hydrogen atoms to give each carbon atom four bonds, we obtain structure (1).

(1) [latex]\begin{matrix}\ \ \ \ \ \ \ \ \underset{|}{H} \ \ \ \ \underset{|}{H} \ \ \ \ \underset{|}{H} \ \ \ \ \ \underset{|}{H} \ \ \ \ \ \underset{|}{H} \ \ \ \ \ \ \ \ H-C-C-C-C-C-H\ \ \ \ \ \ \ \ \ \overset{|}{H} \ \ \ \ \overset{|}{H} \ \ \ \ \overset{|}{H} \ \ \ \ \ \overset{|}{H} \ \ \ \ \ \overset{|}{H} \ \ \ \ \ \ \ \ \ \ \end{matrix} [/latex]

Now, let's look for isomers with four C atoms in the longest chain and one C atom as a branch (five C atoms in all). There is only one possibility. Notice that if structure (2) is flipped from left to right, the identical structure (2') is obtained.

(2) [latex]\begin{matrix} \underset{|}{C} \ \ \ \ \ \ \ \ C-C-C-C\ \end{matrix} [/latex] (2') [latex]\begin{matrix} \ \ \ \ \ \ \ \ \ \ \underset{|}{C} \ \ C-C-C-C\ \end{matrix} [/latex]

Again, we complete the structure of this isomer by adding H atoms.

[latex]\begin{matrix}\ \ \ \ \ \ \ \ \ \underset{|}{H}\ \ \underset{|}{CH_3} \ \ \underset{|}{H} \ \ \ \ \ \underset{|}{H} \ \ \ \ \ \ \ \ \ H-C-C-C-C-H\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \overset{|}{H} \ \ \ \ \overset{|}{H} \ \ \ \ \ \overset{|}{H} \ \ \ \ \overset{|}{H} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \end{matrix} [/latex]

Finally, let's consider a three-carbon chain with two onecarbon branches. Again, there is only one possibility.

The number of isomers with the formula [latex]C_5H_{12}[/latex] is three.

[latex]\begin{matrix} \underset{|}{C} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ C-C-C \quad ext{ that is,} \ \overset{|}{C} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \end{matrix} \begin{matrix} \ \ \ \ \underset{|}{CH_3} \ \quad CH_3-C-CH_3 \ \ \ \ \ \overset{|}{CH_3} \ \ \end{matrix}[/latex]

Assess
We must be careful to recognize when two possible structures are actually the same structure, as was the case for structures (2) and (2').

Question 26.1: Identifying Isomers Write structural formulas for all the co...

Related Answered Questions

Writing the Formula to Correspond to the Name of an Alkane Hydrocarbon Write a condensed structural formula for 4-tert-butyl-2-methylheptane. Analyze The name tells us that the compound is a heptane with two substituent groups, tert-butyl and methyl, positioned at carbons 4 and 2, respectively. ...

Verified Answer:

Choosing the Most Stable Conformer of an Alkane Draw the conformation of 2,3-dimethylpentane that is lowest in energy when the molecule is viewed along C2—C3 axis. Analyze We must first draw a structural diagram for the molecule and identify the C2—C3 axis and then draw a Newman projection ...

Verified Answer:

Identifying Chiral Carbon Atoms in Cycloalkanes Identify any chiral carbon atoms in the molecules to the right. Analyze A carbon atom is chiral if it is bonded to four different groups. To determine whether a carbon atom in a ring structure is chiral, we must go around the ring in each direction ...

Verified Answer:

Verified Answer:

Determining the Degree of Unsaturation and Suggesting Possible Structures for a Molecule What different types of compounds are possible for a compound with the molecular formula C6H10O? Analyze We need to establish the degree of unsaturation in the molecule and then construct one example of each ...

Verified Answer:

Verified Answer:

Identifying a Chiral Molecule Predict whether either 2-chloropentane or 3-chloropentane is chiral. Analyze To decide whether a molecule is chiral, we look for a C atom that has four different groups attached. ...

Verified Answer:

Predicting Which Conformer of a Disubstituted Cycloalkane Is Lowest in Energy Draw the lowest energy conformation of cis-1,3-dimethylcyclohexane. Analyze First, we draw a cyclohexane ring showing both the axial and the equatorial bonds but without the substituents added to the ring. Then, we ...

Verified Answer:

Naming an Alkane Hydrocarbon Give an appropriate IUPAC name for the following compound, an important constituent of gasoline. Analyze We apply the rules listed above. With practice, you will be able to apply the rules without referring back to the list. ...

Verified Answer:

Verified Answer: