Chapter 19, Problem 19.4P

Interpretation Introduction

(a)

Interpretation:

A suitable structure for ${\text{C}}_{\text{4}}{\text{H}}_{\text{8}}\text{O}$ that is in accordance with the given spectroscopic data is to be stated.

Concept introduction:

Spectroscopy method is used to identify the structure of the molecule. It is based on the interactions between matter and electromagnetic radiations. IR spectroscopy is used for the detection of functional group present in the compound. 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 19.4P

A suitable structure for ${\text{C}}_{\text{4}}{\text{H}}_{\text{8}}\text{O}$ that is in accordance with the given spectroscopic data is shown below.

Explanation of Solution

The degree of unsaturation or double bond equivalent (DBE) is calculated by the formula stated below.

$\text{DBE}=\text{C+1}-\frac{\text{H}}{\text{2}}-\frac{\text{X}}{\text{2}}\text{+}\frac{\text{N}}{\text{2}}$ …(1)

Where,

• $\text{C}$ is the number of carbon atoms.
• $\text{H}$ is the number of hydrogen atoms.
• $\text{X}$ is the number of halogen atoms.
• $\text{N}$ is the number of nitrogen atoms.

For ${\text{C}}_{\text{4}}{\text{H}}_{\text{8}}\text{O}$, substitute $\text{C}$ as $4$, $\text{H}$ as $8$ and $\text{N, X}$ as zero in equation (1).

$\begin{array}{rll}\text{DBE}& =& \text{4+1}-\frac{8}{\text{2}}-\frac{0}{\text{2}}\text{+}\frac{0}{\text{2}}\\ & =& 5-4\\ & =& 1\end{array}$

The value of DBE indicates that either there is a double bond or a ring. The IR band at $\text{1720}{\text{cm}}^{-1}$ indicates the presence of carbonyl group $\left(\text{C=O}\right)$. The IR band at $\text{2710}{\text{cm}}^{-1}$ indicates the presence of the aldehydic proton. So, the functional group present is aldehyde.

The proton NMR spectra of this compound is shown below.

Figure 1

The proton NMR data confirms the presence of aldehydic proton with a singlet peak at $\text{δ9}\text{.65}$ for a single hydrogen. The septet observed at around $\text{δ2}\text{.5}$ for one hydrogen suggests that two methyl groups are attached to the carbon. The doublet observed at around $\text{δ1}$ for six hydrogens confirms the presence of two methyl groups.

Therefore a suitable structure of ${\text{C}}_{\text{4}}{\text{H}}_{\text{8}}\text{O}$ is shown below.

Figure 2

Conclusion

A suitable structure for ${\text{C}}_{\text{4}}{\text{H}}_{\text{8}}\text{O}$ that is in accordance with the given spectroscopic data is shown in Figure 2.

Interpretation Introduction

(b)

Interpretation:

A suitable structure for ${\text{C}}_{\text{4}}{\text{H}}_{\text{8}}\text{O}$ that is in accordance with the given spectroscopic data is to be stated.

Concept introduction:

Spectroscopy method is used to identify the structure of the molecule. It is based on the interactions between matter and electromagnetic radiations. IR spectroscopy is used for the detection of functional group present in the compound. 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 19.4P

A suitable structure for ${\text{C}}_{\text{4}}{\text{H}}_{\text{8}}\text{O}$ that is in accordance with the given spectroscopic data is shown below.

Explanation of Solution

The degree of unsaturation or double bond equivalent (DBE) is calculated by the formula stated below.

$\text{DBE}=\text{C+1}-\frac{\text{H}}{\text{2}}-\frac{\text{X}}{\text{2}}\text{+}\frac{\text{N}}{\text{2}}$ …(1)

Where,

• $\text{C}$ is the number of carbon atoms.
• $\text{H}$ is the number of hydrogen atoms.
• $\text{X}$ is the number of halogen atoms.
• $\text{N}$ is the number of nitrogen atoms.

For ${\text{C}}_{\text{4}}{\text{H}}_{\text{8}}\text{O}$, substitute $\text{C}$ as $4$, $\text{H}$ as $8$ and $\text{N, X}$ as zero in equation (1).

$\begin{array}{rll}\text{DBE}& =& \text{4+1}-\frac{8}{\text{2}}-\frac{0}{\text{2}}\text{+}\frac{0}{\text{2}}\\ & =& 5-4\\ & =& 1\end{array}$

The value of DBE indicates that either there is a double bond or a ring. The IR band at $\text{1717}{\text{cm}}^{-1}$ indicates the presence of carbonyl group $\text{C=O}$, as there is no peak for aldehydic proton in the NMR data, therefore ketonic group is expected. The proton NMR data confirms the presence of ketone group as there is a singlet peak for three hydrogens suggesting the presence of methyl group attached to ketonic carbon.

Therefore a suitable structure of ${\text{C}}_{\text{4}}{\text{H}}_{\text{8}}\text{O}$ is shown below.

Figure 3

Conclusion

A suitable structure for ${\text{C}}_{\text{4}}{\text{H}}_{\text{8}}\text{O}$ that is in accordance with the given spectroscopic data is shown in Figure 3.

Interpretation Introduction

(c)

Interpretation:

A suitable structure for the compound that is in accordance with the given spectroscopic data is to be stated.

Concept introduction:

Spectroscopy method is used to identify the structure of the molecule. It is based on the interactions between matter and electromagnetic radiations. IR spectroscopy is used for the detection of functional group present in the compound. 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 19.4P

A suitable structure for compound that is in accordance with the given spectroscopic data is shown below.

Explanation of Solution

The molecular mass of the compound is $\text{70}\text{.1}\text{g}$.In the NMR data, the peak at $\text{δ2}\text{.01}$ is a quintuplet which indicates the presence of four protons in a manner as shown below.

${\text{CH}}_{\text{2}}{\text{-CH}}_{\text{2}}^{·}{\text{-CH}}_{\text{2}}$

The peak at $\text{δ3}\text{.09}$ is a triplet indicating the presence of two hydrogens in a manner as shown below.

${\text{CH}}_{\text{2}}{\text{-CH}}_{\text{2}}^{·}$

So, the number of protons can be six.

The IR data suggests the presence of a carbonyl group because of the IR peak at $\text{1780}{\text{cm}}^{\text{-1}}$. There is no peak for aldehydic proton in the NMR data, therefore ketonic group is confirmed

Therefore the molecular formula of the above compound can be ${\text{C}}_{\text{4}}{\text{H}}_{\text{6}}\text{O}$.

The degree of unsaturation or double bond equivalent (DBE) is calculated by the formula stated below.

$\text{DBE}=\text{C+1}-\frac{\text{H}}{\text{2}}-\frac{\text{X}}{\text{2}}\text{+}\frac{\text{N}}{\text{2}}$ …(1)

Where,

• $\text{C}$ is the number of carbon atoms.
• $\text{H}$ is the number of hydrogen atoms.
• $\text{X}$ is the number of halogen atoms.
• $\text{N}$ is the number of nitrogen atoms.

For ${\text{C}}_{\text{4}}{\text{H}}_6\text{O}$, substitute $\text{C}$ as $4$, $\text{H}$ as $6$ and $\text{N, X}$ as zero in equation (1).

$\begin{array}{rll}\text{DBE}& =& \text{4+1}-\frac{6}{\text{2}}-\frac{0}{\text{2}}\text{+}\frac{0}{\text{2}}\\ & =& 5-3\\ & =& 2\end{array}$

The value of DBE indicates that either there is a double bond and a ring or two double bonds or two rings.

The high value of IR carbonyl frequency indicates the presence of highly strained ring.

Therefore a suitable structure of ${\text{C}}_{\text{4}}{\text{H}}_6\text{O}$ is shown below.

Figure 4

Conclusion

A suitable structure for ${\text{C}}_{\text{4}}{\text{H}}_6\text{O}$ that is in accordance with the given spectroscopic data is shown in Figure 4.

Interpretation Introduction

(d)

Interpretation:

A suitable structure for ${\text{C}}_{10}{\text{H}}_{12}{\text{O}}_2$ that is in accordance with the given spectroscopic data is to be stated.

Concept introduction:

Spectroscopy method is used to identify the structure of the molecule. It is based on the interactions between matter and electromagnetic radiations. IR spectroscopy is used for the detection of functional group present in the compound. 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 19.4P

A suitable structure for ${\text{C}}_{10}{\text{H}}_{12}{\text{O}}_2$ that is in accordance with the given spectroscopic data is shown below.

Explanation of Solution

The degree of unsaturation or double bond equivalent (DBE) is calculated by the formula stated below.

$\text{DBE}=\text{C+1}-\frac{\text{H}}{\text{2}}-\frac{\text{X}}{\text{2}}\text{+}\frac{\text{N}}{\text{2}}$ …(1)

Where,

• $\text{C}$ is the number of carbon atoms.
• $\text{H}$ is the number of hydrogen atoms.
• $\text{X}$ is the number of halogen atoms.
• $\text{N}$ is the number of nitrogen atoms.

For ${\text{C}}_{10}{\text{H}}_{12}{\text{O}}_2$, substitute $\text{C}$ as $10$, $\text{H}$ as $12$ and $\text{N, X}$ as zero in equation (1).

$\begin{array}{rll}\text{DBE}& =& \text{10+1}-\frac{12}{\text{2}}-\frac{0}{\text{2}}\text{+}\frac{0}{\text{2}}\\ & =& 11-6\\ & =& 5\end{array}$

The value of DBE indicates the presence of four double bonds and a ring. The IR absorption peak at $\text{1690}{\text{cm}}^{\text{-1}}$ indicates the presence of a ketonic group as there is no peak for aldehydic proton in the NMR data. The peak at $\text{1612}{\text{cm}}^{\text{-1}}$ confirms the presence of an aromatic ring.

The proton NMR data confirms the presence of ketone group as there is a singlet peak for three hydrogensat $\text{δ2}\text{.5}$. The downfield value of proton at $\text{δ6}\text{.9}$ suggests the presence of carbonyl group attached to the benzene ring. The high value of the protons $\text{δ1}\text{.4}$ and $\text{δ4}\text{.1}$ indicates the attachment of oxygen group.

Therefore a suitable structure of ${\text{C}}_{10}{\text{H}}_{12}{\text{O}}_2$ is shown below.

Figure 5

Conclusion

A suitable structure for ${\text{C}}_{10}{\text{H}}_{12}{\text{O}}_2$ that is in accordance with the given spectroscopic data is shown in Figure 5.