Chapter 12, Problem 12.27AP

Interpretation Introduction

Interpretation:

The following compounds are to be matched with their respective IR spectra.

(a) $1,5-\text{hexadiene}$

(b) $1-$ methylcyclopentene

(c) $1-\text{hexen}-3-\text{ol}$

(d) dipropyl ether

(e) $trans-4-\text{octene}$

(f) cyclohexane

(g) $3-\text{hexanol}$

Concept introduction:

The IR spectrum of a compound shows absorptions at different frequencies. These absorption frequencies depend upon the bond stretching frequency of the bonds in molecule.

Answer to Problem 12.27AP

The matching of the given compounds with their respective IR spectra is shown in the table below.

Compounds	IR spectra
a. $1,5-\text{hexadiene}$
b. $1-$ methylcyclopentene
c. $1-\text{hexen}-3-\text{ol}$
d. dipropyl ether
e. $trans-4-\text{octene}$	No IR spectrum available.
f. cyclohexane
g. $3-\text{hexanol}$	No IR spectrum available.

Explanation of Solution

(a) The given compound is $1,5-\text{hexadiene}$ as shown below.

Figure 1

In the IR spectra of $1,5-\text{hexadiene}$, a intense peak for $\text{C}=\text{C}$ stretching is shown at $1620{\text{cm}}^{-1}$ and another strong peak for $=\text{C}-\text{H}$ stretching is shown at $\text{3100}{\text{cm}}^{-1}$. Due the presence of the vinyl, $=\text{C}-\text{H}$, bend, the absorptions peaks are shown at $9\text{10}{\text{cm}}^{-1}$ and $9\text{90}{\text{cm}}^{-1}$. This absorption peaks indicates that the given compound is a terminal alkene. So, the corresponding IR spectrum for $1,5-\text{hexadiene}$ is shown below.

Figure 2

(b) The given compound is $1-$ methylcyclopentene as shown below.

Figure 3

In the IR spectra of $1-$ methylcyclopentene, a intense peak for $\text{C}=\text{C}$ stretching is shown at $1660{\text{cm}}^{-1}$ and another strong peak for $=\text{C}-\text{H}$ stretching is shown at $\text{3010}{\text{cm}}^{-1}$. Due the presence of the vinyl, $=\text{C}-\text{H}$, bend, the absorptions peaks are shown at $80\text{0}{\text{cm}}^{-1}$. So, the corresponding IR spectrum for $1-$ methylcyclopentene is shown below.

Figure 4

(c) The given compound is $1-\text{hexen}-3-\text{ol}$ as shown below.

Figure 5

In the IR spectra of $1-\text{hexen}-3-\text{ol}$, a broad peak for $\text{O}-\text{H}$ stretching is shown at $3200{\text{cm}}^{-1}-3400{\text{cm}}^{-1}$ and another strong peak for $=\text{C}-\text{H}$ stretching is shown at $\text{3080}{\text{cm}}^{-1}$. Due the presence of the vinyl bend, the absorptions peaks are shown at $91\text{0}{\text{cm}}^{-1}$ and $91\text{0}{\text{cm}}^{-1}$. So, the corresponding IR spectrum for $1-\text{hexen}-3-\text{ol}$ is shown below.

Figure 6

(d) The given compound is dipropyl ether, ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}-\text{O}-{\text{CH}}_{\text{2}}{\text{CH}}_{\text{3}}$. In the IR spectra of dipropyl ether, a strong peak for $\text{C}-\text{O}$ stretching is shown at $1100{\text{cm}}^{-1}$. So, the corresponding IR spectrum for dipropyl ether is shown below.

Figure 7

(e) The IR spectrum for $trans-4-\text{octene}$ is not available for matching.

(f) The given compound is cyclohexane as shown below.

Figure 8

In the IR spectra of cyclohexane, a strong absorption peak for $\text{C}-\text{H}$ stretching is shown at $2800{\text{cm}}^{-1}-2900{\text{cm}}^{-1}$. There is no other functional group is present in cyclohexane. So, the corresponding IR spectrum for cyclohexane is shown below.

Figure 9

(g) The IR spectrum for $trans-4-\text{octene}$ is not available for matching.

Conclusion

(a) The spectrum 2 corresponds to the compound, $1,5-\text{hexadiene}$.

(b) The spectrum 5 corresponds to the compound, $1-$ methylcyclopentene.

(c) The spectrum 4 corresponds to the compound, $1-\text{hexen}-3-\text{ol}$.

(d) The spectrum 1 corresponds to the compound, dipropyl ether.

(e) There is no spectrum available for the compound, $trans-4-\text{octene}$.

(f) The spectrum 3 corresponds to the compound, cyclohexane.

(g) There is no spectrum available for the compound, $3-\text{hexanol}$.