Chapter 22, Problem 22.75P

Identify the structures of each compound from the given data.

a. Molecular formula ${\text{C}}_{\text{6}}{\text{H}}_{\text{12}}{\text{O}}_{\text{2}}$

IR absorption: $1738{\text{cm}}^{-1}$

${}^{\text{1}}\text{H}$ NMR: $1.12$ (triplet, $\text{3}\text{H}$), $1.23$ (doublet, $\text{6}\text{H}$), $2.28$

(quartet, $\text{2}\text{H}$), and $5.00$ (septet, $\text{1}\text{H}$) ppm

b. Molecular formula ${\text{C}}_{\text{4}}{\text{H}}_{\text{7}}\text{N}$

IR absorption: $2250{\text{cm}}^{-1}$

${}^{\text{1}}\text{H}$ NMR: $1.08$ (triplet, $\text{3}\text{H}$), $1.70$ (multiplet, $\text{2}\text{H}$) and $2.34$

(triplet, $\text{2}\text{H}$) ppm

c. Molecular formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{9}}\text{NO}$

IR absorption: $3328{\text{cm}}^{-1}$ and $1639{\text{cm}}^{-1}$

${}^{\text{1}}\text{H}$ NMR: $2.95$ (singlet, $\text{3}\text{H}$), $6.95$ (singlet, $\text{1}\text{H}$) and

$7.3-7.7$ (multiplet, $\text{5}\text{H}$) ppm

d. Molecular formula ${\text{C}}_{\text{4}}{\text{H}}_{\text{7}}\text{ClO}$

IR absorption: $1802{\text{cm}}^{-1}$

${}^{\text{1}}\text{H}$ NMR: $0.95$ (triplet, $\text{3}\text{H}$), $1.07$ (multiplet, $\text{2}\text{H}$) and $2.90$

(triplet, $\text{2}\text{H}$) ppm

e. Molecular formula ${\text{C}}_{\text{10}}{\text{H}}_{\text{12}}{\text{O}}_2$

IR absorption: $1740{\text{cm}}^{-1}$

${}^{\text{1}}\text{H}$ NMR: $1.2$ (triplet, $\text{3}\text{H}$), $2.4$ (quartet, $\text{2}\text{H}$), $5.1$ (singlet,

$\text{2}\text{H}$), and $7.1-7.5$ (multiplet, $\text{5}\text{H}$) ppm

Interpretation Introduction

(a)

Interpretation: The structure of compound that has molecular formula ${\text{C}}_{\text{6}}{\text{H}}_{\text{12}}{\text{O}}_{\text{2}}$ is to be identified from the given data.

Concept introduction: The method of spectroscopy is used to identify the structure of the molecule. It is based on the interactions between matter and electromagnetic radiations. Proton NMR spectroscopy identifies the number of hydrogen atoms present in a molecule and the nature of the functional group. The value of chemical peaks depends upon the chemical environment around the hydrogen atom.

Answer to Problem 22.75P

The structure of given compound is,

Explanation of Solution

The IR absorption value of the given compound is $1738{\text{cm}}^{-1}$ which corresponds to that of an ester. Hence, the given compound contains ester linkage.

A septet of one hydrogen atoms at $5.00\text{ppm}$ shows that this carbon atom is directly bonded to electronegative oxygen atom of ester and to two methyl groups. A doublet of six hydrogen atoms is due to this hydrogen atom.

A triplet peak of three hydrogen atoms and a quartet of two carbon atoms shows that their carbon atoms are bonded to each other and the splitting peak takes place according to $n+1$ rule.

Therefore, the structure of compound is,

Figure 1

Conclusion

The structure of given compound is shown in Figure 1.

Interpretation Introduction

(b)

Interpretation: The structure of compound that has molecular formula ${\text{C}}_{\text{4}}{\text{H}}_{\text{7}}\text{N}$ is to be identified from the given data.

Concept introduction: The method of spectroscopy is used to identify the structure of the molecule. It is based on the interactions between matter and electromagnetic radiations. Proton NMR spectroscopy identifies the number of hydrogen atoms present in a molecule and the nature of the functional group. The value of chemical peaks depends upon the chemical environment around the hydrogen atom.

Answer to Problem 22.75P

The structure of given compound is,

Explanation of Solution

The IR absorption value of the given compound is $2250{\text{cm}}^{-1}$ which corresponds to that of a nitrile group. Hence, the given compound contains nitrile group.

In the given compound, one out of four carbon atoms is ${}^{\text{1}}\text{H}$ NMR inactive. A triplet of two and three hydrogen atoms at $2.34\text{ppm}$ and $1.08\text{ppm}$, respectively, shows that their carbon atoms are bonded to carbon atom that contains two hydrogen atoms. On the other hand, the carbon atom that contains two hydrogen atoms give multiplet at $1.70\text{ppm}$. A carbon atom, that gives NMR peak at $2.34\text{ppm}$, is bonded to nitrile group.

Therefore, the structure of compound is,

Figure 2

Conclusion

The structure of given compound is shown in Figure 2.

Interpretation Introduction

(c)

Interpretation: The structure of compound that has molecular formula ${\text{C}}_{\text{8}}{\text{H}}_{\text{9}}\text{NO}$ is to be identified from the given data.

Concept introduction: The method of spectroscopy is used to identify the structure of the molecule. It is based on the interactions between matter and electromagnetic radiations. Proton NMR spectroscopy identifies the number of hydrogen atoms present in a molecule and the nature of the functional group. The value of chemical peaks depends upon the chemical environment around the hydrogen atom.

Answer to Problem 22.75P

The structure of given compound is,

Explanation of Solution

The IR absorption value of the given compound are $3328{\text{cm}}^{-1}$ and $1639{\text{cm}}^{-1}$, which corresponds to those of an $\text{N}-\text{H}$ bond and an amide linkage, respectively.

Multiple ${}^{\text{1}}\text{H}$ NMR peaks of five hydrogen atoms, between $7.3\text{ppm}-7.7\text{ppm}$, shows that an aromatic ring is substituted by one group. A singlet peak of three hydrogen atoms shows that this carbon atom is bonded to electronegative ${}^{\text{1}}\text{H}$ NMR inactive atom.

A singlet NMR peak of one hydrogen atom is observed due to presence of $\text{N}-\text{H}$ bond.

Therefore, the structure of compound is,

Figure 3

Conclusion

The structure of given compound is shown in Figure 3.

Interpretation Introduction

(d)

Interpretation: The structure of compound that has molecular formula ${\text{C}}_{\text{4}}{\text{H}}_{\text{7}}\text{ClO}$ is to be identified from the given data.

Concept introduction: The method of spectroscopy is used to identify the structure of the molecule. It is based on the interactions between matter and electromagnetic radiations. Proton NMR spectroscopy identifies the number of hydrogen atoms present in a molecule and the nature of the functional group. The value of chemical peaks depends upon the chemical environment around the hydrogen atom.

Answer to Problem 22.75P

The structure of given compound is,

Explanation of Solution

The IR absorption value of the given compound is $1802{\text{cm}}^{-1}$ which corresponds to that of an acid chloride.

In the given compound, one out of four carbon atoms is ${}^{\text{1}}\text{H}$ NMR inactive. A triplet of two and three hydrogen atoms at $2.90\text{ppm}$ and $0.95\text{ppm}$, respectively, shows that their carbon atoms are bonded to carbon atom that contains two hydrogen atoms. On the other hand, the carbon atom that contains two hydrogen atoms give multiple at $1.07\text{ppm}$. A carbon atom, that gives NMR peak at $2.90\text{ppm}$ is bonded to carbonyl group.

Therefore, the structure of compound is,

Figure 4

Conclusion

The structure of given compound is shown in Figure 4.

Interpretation Introduction

(e)

Interpretation: The structure of compound that has molecular formula ${\text{C}}_{\text{10}}{\text{H}}_{\text{12}}{\text{O}}_{\text{2}}$ is to be identified from the given data.

Concept introduction: The method of spectroscopy is used to identify the structure of the molecule. It is based on the interactions between matter and electromagnetic radiations. Proton NMR spectroscopy identifies the number of hydrogen atoms present in a molecule and the nature of the functional group. The value of chemical peaks depends upon the chemical environment around the hydrogen atom.

Answer to Problem 22.75P

The structure of given compound is,

Explanation of Solution

The IR absorption value of the given compound is $1740{\text{cm}}^{-1}$ which corresponds to that of an ester. Hence, the given compound contains an ester linkage.

Multiple ${}^{\text{1}}\text{H}$ NMR peaks of five hydrogen atoms, between $7.1\text{ppm}-7.5\text{ppm}$, shows that an aromatic ring is substituted by one group. A singlet peak of two hydrogen atoms at $5.1\text{ppm}$ shows that, this carbon atom is bonded to two electronegative ${}^{\text{1}}\text{H}$ NMR inactive atoms. A triplet peak of three hydrogen atoms and a quartet of two carbon atoms shows that their carbon atoms are bonded to each other and the splitting peak takes place according to $n+1$ rule.

Therefore, the structure of compound is,

Figure 5

Conclusion

The structure of given compound is shown in Figure 5.