Chapter 15, Problem 38PP

a)

Interpretation Introduction

Interpretation:

For the given compounds that absorbing the IR radiation in the range between 1600and 1850 $c{m}^{-1}$, the specific bonds responsible for the absorptions should be identified and the approximate wave number of absorption for each of those bonds should be predicted.

Concept introduction:

Compounds that absorbing the IR radiation in the range between 1600and 1850 $c{m}^{-1}$ should be associated with at least one double bond or more than one double bond are responsible for the absorption.

Reciprocal of wavelength is called wavenumber or Number of waves in one centimeter is called wavenumber

Unit of wave number is reciprocal of Centimeter.

According to Hooke’s law the factors affecting wave numbers are

1. Bond strength

2. Reduced mass

$\begin{array}{l}\overline{\text{ν}}\text{=}\left(\frac{\text{1}}{\text{2πc}}\right){\left(\frac{\text{f}}{{\text{m}}_{\text{red}}}\right)}^{\text{1/2}}\\ \text{f}\text{=}\text{force}\text{constant}\left(\text{bond}\text{strength}\right)\\ {\text{m}}_{\text{red}}\text{=}\text{reduced}\text{mass}\\ \text{=}\frac{{\text{m}}_{\text{1}}{\text{m}}_{\text{2}}}{{\text{m}}_{\text{1}}{\text{+m}}_{\text{2}}}\end{array}$

The conjugated compound produces a signal at lower wavenumber, because it has some single bond character and possess weak bond due to resonance.

To find: the responsible bonds for the IR absorption and wave number of the given compound

Answer to Problem 38PP

The responsible bonds for IR absorption and the wavenumber of the given compound in the IR radiation range between 1600and1850 $c{m}^{-1}$ are,

Explanation of Solution

For the given compound A the responsible bonds are,

Conjugated carbonyl and conjugated C=C bonds.

For the conjugated carbonyl bond approximate wavenumber is 1680 $c{m}^{-1}$

For the conjugated C=C bond approximate wavenumber is 1600 $c{m}^{-1}$

For unsaturated or conjugated carbonyl compound there is an introduction of C=C bond separated by one sigma bond.

In conjugated system $\pi$ bonds are separated by one sigma bond. Conjugated carbonyl compound produces signal at lower wavenumber of 1680 $c{m}^{-1}$ than that of isolated or non-conjugated carbonyl compound of 1720 $c{m}^{-1}$. The reason behind it is conjugated carbonyl bond has single bond character due to resonance and therefore this bond is merely weaker.

  In the case of conjugated C=C bond, $\pi$ bonds are separated by one sigma bond. The unsaturated or conjugated C=C bond produces a signal at lower wavenumber of 1600 $c{m}^{-1}$. The reason behind it is conjugated C=C bond has single bond character due to resonance and therefore this bond is merely weaker.

(b)

Interpretation Introduction

Interpretation:

For the given compounds that absorbing the IR radiation in the range between 1600and 1850 $c{m}^{-1}$, the specific bonds responsible for the absorptions should be identified and the approximate wave number of absorption for each of those bonds should be predicted.

Concept introduction:

Compounds that absorbing the IR radiation in the range between 1600and 1850 $c{m}^{-1}$ should be associated with at least one double bond or more than one double bond are responsible for the absorption.

Reciprocal of wavelength is called wavenumber or Number of waves in one centimeter is called wavenumber

Unit of wave number is reciprocal of Centimeter.

According to Hooke’s law the factors affecting wave numbers are

1. Bond strength

2. Reduced mass

$\begin{array}{l}\overline{\text{ν}}\text{=}\left(\frac{\text{1}}{\text{2πc}}\right){\left(\frac{\text{f}}{{\text{m}}_{\text{red}}}\right)}^{\text{1/2}}\\ \text{f}\text{=}\text{force}\text{constant}\left(\text{bond}\text{strength}\right)\\ {\text{m}}_{\text{red}}\text{=}\text{reduced}\text{mass}\\ \text{=}\frac{{\text{m}}_{\text{1}}{\text{m}}_{\text{2}}}{{\text{m}}_{\text{1}}{\text{+m}}_{\text{2}}}\end{array}$

The conjugated compound produces a signal at lower wavenumber, because it has some single bond character and possess weak bond due to resonance.

To find: the responsible bonds for the IR absorption and wave number of the given compound

Answer to Problem 38PP

The responsible bonds for IR absorption and the wavenumber of the given compound in the IR radiation range between 1600and1850 $c{m}^{-1}$ are,

Explanation of Solution

For the given compound B the responsible bonds are

Isolated carbonyl and C=C bonds.

For isolated or saturated carbonyl bond, approximate wavenumber is 1720 $c{m}^{-1}$

For isolated or saturated   C=C bond, approximate wavenumber is 1650 $c{m}^{-1}$

Isolated carbonyl group has mostly double bond character.

 So, isolated carbonyl compounds produces signal at higher wavenumber of 1720 $c{m}^{-1}$ than that of conjugated carbonyl compound of 1680 $c{m}^{-1}$.

Like the same way, Isolated C=C has mostly double bond character

So, isolated C=C produces signal at higher wavenumber of 1650 $c{m}^{-1}$ than that of conjugated C=C bond of 1600 $c{m}^{-1}$.

(c)

Interpretation Introduction

Interpretation:

For the given compounds that absorbing the IR radiation in the range between 1600and 1850 $c{m}^{-1}$, the specific bonds responsible for the absorptions should be identified and the approximate wave number of absorption for each of those bonds should be predicted.

Concept introduction:

Compounds that absorbing the IR radiation in the range between 1600and 1850 $c{m}^{-1}$ should be associated with at least one double bond or more than one double bond are responsible for the absorption.

Reciprocal of wavelength is called wavenumber or Number of waves in one centimeter is called wavenumber

Unit of wave number is reciprocal of Centimeter.

According to Hooke’s law the factors affecting wave numbers are

1. Bond strength

2. Reduced mass

$\begin{array}{l}\overline{\text{ν}}\text{=}\left(\frac{\text{1}}{\text{2πc}}\right){\left(\frac{\text{f}}{{\text{m}}_{\text{red}}}\right)}^{\text{1/2}}\\ \text{f}\text{=}\text{force}\text{constant}\left(\text{bond}\text{strength}\right)\\ {\text{m}}_{\text{red}}\text{=}\text{reduced}\text{mass}\\ \text{=}\frac{{\text{m}}_{\text{1}}{\text{m}}_{\text{2}}}{{\text{m}}_{\text{1}}{\text{+m}}_{\text{2}}}\end{array}$

The conjugated compound produces a signal at lower wavenumber, because it has some single bond character and possess weak bond due to resonance.

To find: the responsible bonds for the IR absorption and wave number of the given compound

Answer to Problem 38PP

The responsible bonds for IR absorption and the wavenumber of the given compound in the IR radiation range between 1600and1850 $c{m}^{-1}$ are,

Explanation of Solution

For the given compound C the responsible bond is,

Carbonyl bond of an ester

For isolated or saturated carbonyl bond of an ester, the approximate wavenumber is 1740 $c{m}^{-1}$.

Isolated or saturated ester produces the signal of higher wave number than that of conjugated or unsaturated ester of 1700 $c{m}^{-1}$

(d)

Interpretation Introduction

Interpretation:

For the given compounds that absorbing the IR radiation in the range between 1600and 1850 $c{m}^{-1}$, the specific bonds responsible for the absorptions should be identified and the approximate wave number of absorption for each of those bonds should be predicted.

Concept introduction:

Compounds that absorbing the IR radiation in the range between 1600and 1850 $c{m}^{-1}$ should be associated with at least one double bond or more than one double bond are responsible for the absorption.

Reciprocal of wavelength is called wavenumber or Number of waves in one centimeter is called wavenumber

Unit of wave number is reciprocal of Centimeter.

According to Hooke’s law the factors affecting wave numbers are

1. Bond strength

2. Reduced mass

$\begin{array}{l}\overline{\text{ν}}\text{=}\left(\frac{\text{1}}{\text{2πc}}\right){\left(\frac{\text{f}}{{\text{m}}_{\text{red}}}\right)}^{\text{1/2}}\\ \text{f}\text{=}\text{force}\text{constant}\left(\text{bond}\text{strength}\right)\\ {\text{m}}_{\text{red}}\text{=}\text{reduced}\text{mass}\\ \text{=}\frac{{\text{m}}_{\text{1}}{\text{m}}_{\text{2}}}{{\text{m}}_{\text{1}}{\text{+m}}_{\text{2}}}\end{array}$

The conjugated compound produces a signal at lower wavenumber, because it has some single bond character and possess weak bond due to resonance.

To find: the responsible bonds for the IR absorption and wave number of the given compound

Answer to Problem 38PP

The responsible bonds for IR absorption and the wavenumber of the given compound in the IR radiation range between 1600and1850 $c{m}^{-1}$ are,

Explanation of Solution

For the given compound D the responsible bonds are,

 Conjugated carbonyl bond of an ester

 Conjugated C=C bond.

 For conjugated carbonyl bond of an ester, the approximate wavenumber is 1700 $c{m}^{-1}$.

For the conjugated C=C bond approximate wavenumber is 1600 $c{m}^{-1}$

Conjugated or unsaturated ester produces the signal of lower wave number than that of Isolated or saturated ester. In conjugated system $\pi$ bonds are separated by one sigma bond.

The reason behind it is conjugated carbonyl bond of an ester has single bond character due to resonance and therefore this bond is merely weaker.

  In the case of conjugated C=C bond, $\pi$ bonds are separated by one sigma bond. The unsaturated or conjugated C=C bond produces a signal at lower wavenumber of 1600 $c{m}^{-1}$. The reason behind it is conjugated C=C bond has single bond character due to resonance and therefore this bond is merely weaker.

(e)

Interpretation Introduction

Interpretation:

For the given compounds that absorbing the IR radiation in the range between 1600and 1850 $c{m}^{-1}$, the specific bonds responsible for the absorptions should be identified and the approximate wave number of absorption for each of those bonds should be predicted.

Concept introduction:

Compounds that absorbing the IR radiation in the range between 1600and 1850 $c{m}^{-1}$ should be associated with at least one double bond or more than one double bond are responsible for the absorption.

Reciprocal of wavelength is called wavenumber or Number of waves in one centimeter is called wavenumber

Unit of wave number is reciprocal of Centimeter.

According to Hooke’s law the factors affecting wave numbers are

1. Bond strength

2. Reduced mass

$\begin{array}{l}\overline{\text{ν}}\text{=}\left(\frac{\text{1}}{\text{2πc}}\right){\left(\frac{\text{f}}{{\text{m}}_{\text{red}}}\right)}^{\text{1/2}}\\ \text{f}\text{=}\text{force}\text{constant}\left(\text{bond}\text{strength}\right)\\ {\text{m}}_{\text{red}}\text{=}\text{reduced}\text{mass}\\ \text{=}\frac{{\text{m}}_{\text{1}}{\text{m}}_{\text{2}}}{{\text{m}}_{\text{1}}{\text{+m}}_{\text{2}}}\end{array}$

The conjugated compound produces a signal at lower wavenumber, because it has some single bond character and possess weak bond due to resonance.

To find: the responsible bonds for the IR absorption and wave number of the given compound

Answer to Problem 38PP

The responsible bonds for IR absorption and the wavenumber of the given compound in the IR radiation range between 1600and1850 $c{m}^{-1}$ are,

Explanation of Solution

For the given compound E the responsible bond for IR absorption is,

Isolated or saturated   C=C bond.

For isolated or saturated   C=C bond, approximate wavenumber is 1650 $c{m}^{-1}$

Isolated C=C produces signal at higher wavenumber of 1650 $c{m}^{-1}$ than that of conjugated C=C bond of 1600 $c{m}^{-1}$.