Chapter 17, Problem 17.55P

Propose a structure consistent with each set of data.

a. ${\text{C}}_{\text{10}}{\text{H}}_{\text{14}}:\text{IR}\text{absorptions}\text{at}\text{3150}-2850,1600,\text{and}\text{1500}{\text{cm}}^{-1}$

b. ${\text{C}}_9{\text{H}}_{\text{12}}:{}^{13}\text{C}\text{NMR}\text{signals}\text{at}21,127,\text{and}\text{138}\text{ppm}$

c. ${\text{C}}_8{\text{H}}_{\text{10}}:\text{IR}\text{absorptions}\text{at}\text{3108}-2875,1606,\text{and}\text{1496}{\text{cm}}^{-1}$

Interpretation Introduction

(a)

Interpretation: A structure consistent with the given set of data is to be predicted.

Concept introduction: Spectroscopy method 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 17.55P

A structure consistent with the given set of data is shown below.

Explanation of Solution

The given set of $\text{IR}$ data is,

${\text{C}}_{\text{10}}{\text{H}}_{\text{14}}:\text{IR}\text{absorptions}\text{at}\text{3150}-2850,1600,\text{and}\text{1500}{\text{cm}}^{-1}$

Information from $\text{IR}$ data:

The $\text{IR}$ absorption at $3150-2850{\text{cm}}^{-1}$ suggests the presence of ${\text{C}}_{s{p}^2}-\text{H}$, and ${\text{C}}_{s{p}^3}-\text{H}$ bonds, and absorptions at $1500,\text{and}1600{\text{cm}}^{-1}$ suggests the presence of benzene ring.

Information from ${}^1\text{H}\text{NMR}$ data:

The observed chemical shift value at $\sim \text{1}\text{.3}\text{ppm}\left(\text{doublet}\right)$ for $\text{6}\text{H}$ suggests the presence of one $\text{H}$ on the adjacent carbon.

The observed chemical shift value at $\sim \text{2}\text{.4}\text{ppm}\left(\text{singlet}\right)$ for $\text{3}\text{H}$ suggests the presence of one methyl group (no $\text{H}$ on the adjacent carbon) on the benzene ring.

The observed chemical shift value at $\sim \text{3}\text{.2}\text{ppm}\left(\text{septet}\right)$ for $\text{1}\text{H}$ suggests the presence of $\text{3}\text{H's}$ on each of the adjacent two carbons.

The observed chemical shift value at $\sim \text{7}\text{.2}\text{ppm}\left(\text{multiplet}\right)$ for $\text{4}\text{H}$ suggests the presence of $\text{4}\text{H's}$ on the benzene ring.

The possible structure of the compound based on the above analysis is,

Figure 1

Conclusion

A structure consistent with the given set of data is shown in Figure 1.

Interpretation Introduction

(b)

Interpretation: A structure consistent with the given set of data is to be predicted.

Concept introduction: Spectroscopy method 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 17.55P

A structure consistent with the given set of data is shown below.

Explanation of Solution

The given set of ${}^{13}\text{C}\text{NMR}$ data is,

${\text{C}}_9{\text{H}}_{\text{12}}:{}^{13}\text{C}\text{NMR}\text{signals}\text{at}21,127,\text{and}\text{138}\text{ppm}$

Information from ${}^{13}\text{C}\text{NMR}$ data:

Three signals are observed in ${}^{13}\text{C}\text{NMR}$ spectrum. This means three different types of carbon atoms are present in compound.

The ${}^{13}\text{C}\text{NMR}$ signal at $21,127,\text{and}\text{138}\text{ppm}$ suggest the presence of given types of carbon atoms.

Figure 2

Information from ${}^1\text{H}\text{NMR}$ data:

The observed chemical shift value at $\sim \text{2}\text{.3}\text{ppm}\left(\text{singlet}\right)$ for $\text{9}\text{H}$ suggests the presence of three methyl group (no $\text{H}$ on the adjacent carbon) on benzene ring.

The observed chemical shift value at $\sim \text{6}\text{.9}\text{ppm}\left(\text{singlet}\right)$ for $\text{3}\text{H}$ suggests the presence of three deshielded hydrogen atoms on the benzene ring.

The possible structure of the compound based on the above analysis is,

Figure 3

Conclusion

A structure consistent with the given set of data is shown in Figure 3.

Interpretation Introduction

(c)

Interpretation: A structure consistent with the given set of data is to be predicted.

Concept introduction: Spectroscopy method 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 17.55P

A structure consistent with the given set of data is shown below.

Explanation of Solution

The given set of $\text{IR}$ data is,

${\text{C}}_8{\text{H}}_{\text{10}}:\text{IR}\text{absorptions}\text{at}\text{3108}-2875,1606,\text{and}\text{1496}{\text{cm}}^{-1}$

Information from IR data:

The $\text{IR}$ absorption at $\text{3108}-2875{\text{cm}}^{-1}$ suggest the presence of ${\text{C}}_{s{p}^2}-\text{H}$, and ${\text{C}}_{s{p}^3}-\text{H}$ bonds, and absorptions at $1606,\text{and}\text{1496}{\text{cm}}^{-1}$ suggest the presence of benzene ring.

Information from ${}^1\text{H}\text{NMR}$ data:

The observed chemical shift value at $\sim \text{1}\text{.3}\text{ppm}\left(\text{triplet}\right)$ for $\text{3}\text{H}$ suggests the presence of two $\text{H's}$ on the adjacent carbon.

The observed chemical shift value at $\sim \text{2}\text{.7}\text{ppm}\left(\text{quartet}\right)$ for $\text{2}\text{H}$ suggests the presence of three $\text{H's}$ on the adjacent carbon.

The observed chemical shift value at $\sim \text{7}\text{.4}\text{ppm}\left(\text{multiplet}\right)$ for $\text{5}\text{H}$ suggests the presence of five $\text{H's}$ on the benzene ring.

The possible structure of the compound based on the above analysis is,

Figure 4

Conclusion

A structure consistent with the given set of data is shown in Figure 4.