Chapter 17, Problem 17.56P

Propose a structure consistent with each set of data.

a. Compound A:

$\begin{array}{l}\text{Molecular}\text{formula:}{\text{C}}_{\text{8}}{\text{H}}_{\text{10}}\text{O}\\ \text{IR}\text{absorptions}\text{at}\text{3150-2850,}{\text{cm}}^{-\text{1}}\\ {}^1\text{H}\text{NMR}\text{data:}\text{1}\text{.4}\left(\text{triplet,}\text{3}\text{H}\right),3.9\text{5}\left(\text{quartet,}\text{2}\text{H}\right),\\ \text{and}6.8-7.\text{3}\left(\text{multiplet,}\text{5}\text{H}\right)\text{ppm}\end{array}$

b. Compound B:

$\begin{array}{l}\text{Molecular}\text{formula:}{\text{C}}_9{\text{H}}_{\text{10}}{\text{O}}_2\\ \text{IR}\text{absorptions}\text{at}\text{1669}{\text{cm}}^{-\text{1}}\\ {}^1\text{H}\text{NMR}\text{data:}\text{2}\text{.5}\left(\text{singlet,}\text{3}\text{H}\right),3.8\left(\text{singlet,}\text{3}\text{H}\right),6.9\left(\text{doublet,}2\text{H}\right),\\ \text{and}7.9\left(\text{doublet,}2\text{H}\right)\text{ppm}\end{array}$

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 17.56P

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

Explanation of Solution

The given sets of $\text{IR}$ and ${}^1\text{H}\text{NMR}$ data for Compound A are,

$\begin{array}{l}\text{Molecular}\text{formula:}{\text{C}}_{\text{8}}{\text{H}}_{\text{10}}\text{O}\\ \text{IR}\text{absorptions}\text{at}\text{3150-2850,}{\text{cm}}^{-\text{1}}\\ {}^1\text{H}\text{NMR}\text{data:}\text{1}\text{.4}\left(\text{triplet,}\text{3}\text{H}\right),3.9\text{5}\left(\text{quartet,}\text{2}\text{H}\right),\text{and}6.8-7.\text{3}\left(\text{multiplet,}\text{5}\text{H}\right)\text{ppm}\end{array}$

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.

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

The observed chemical shift value at $\text{1}\text{.4}\left(\text{triplet,}\text{3}\text{H}\right)\text{ppm}$ suggests the presence of $\text{2}\text{H's}$ on the adjacent carbon.

The observed chemical shift value at $\text{3}\text{.95}\left(\text{quartet,}\text{2}\text{H}\right)\text{ppm}$ suggests the presence of $\text{3}\text{H's}$ on the adjacent carbon.

The observed chemical shift value at $6.8-7.\text{3}\left(\text{multiplet,}\text{5}\text{H}\right)\text{ppm}$ suggests the presence of $\text{5}\text{H's}$ on the benzene ring.

The possible structure of the Compound A, 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 17.56P

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

Explanation of Solution

The given sets of $\text{IR}$ and ${}^1\text{H}\text{NMR}$ data for Compound B are,

$\begin{array}{l}\text{Molecular}\text{formula:}{\text{C}}_9{\text{H}}_{\text{10}}{\text{O}}_2\\ \text{IR}\text{absorptions}\text{at}\text{1669}{\text{cm}}^{-\text{1}}\\ {}^1\text{H}\text{NMR}\text{data:}\text{2}\text{.5}\left(\text{singlet,}\text{3}\text{H}\right),3.8\left(\text{singlet,}\text{3}\text{H}\right),6.9\left(\text{doublet,}2\text{H}\right),\\ \text{and}7.9\left(\text{doublet,}2\text{H}\right)\text{ppm}\end{array}$

Information from $\text{IR}$ data:

The $\text{IR}$ absorption at $3150-2850{\text{cm}}^{-1}$ suggests the presence of $\text{1669}{\text{cm}}^{-\text{1}}$.

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

The observed chemical shift value at $\text{2}\text{.5}\left(\text{singlet,}\text{3}\text{H}\right)\text{ppm}$ suggests the presence of methyl group with no hydrogen atom on the adjacent carbon.

The observed chemical shift value at $3.8\left(\text{singlet,}\text{3}\text{H}\right)\text{ppm}$ suggests the presence of methyl group with no hydrogen atom on the adjacent carbon.

The observed chemical shift values at $6.9\left(\text{doublet,}2\text{H}\right),\text{and}7.9\left(\text{doublet,}2\text{H}\right)\text{ppm}$, suggest the presence of $\text{4}\text{H's}\left(\text{2}\text{H's}\text{each}\right)$ on the benzene ring.

The possible structure of the Compound B, based on the above analysis is,

Figure 2

Conclusion

A structure consistent with the given set of data is shown in Figure 2.