Chapter 3.4, Problem 3.10CT

(a)

Interpretation Introduction

Interpretation:

The wavelegths corresponding to the strongest IR absorbance for water vapor has to be estimated from the given spectra.

Concept introduction:

• Electromagnetic spectrum is a range of all types of electromagnetic radiation.

• IR Spectroscopy: The bonds between atoms in the molecule stretch and bend, absorbing IR energy and creating the IR spectrum.
• IR spectroscopy is used to identify the functional groups in a compound. The frequencies in IR spectroscopy are reported using a unit called wavenumber and it is represented by $\overline{\nu }$ and their unit is $c{m}^{-1}$ . using wavenumber scale, IR absorptions occurs from $\text{4000}{\text{cm}}^{\text{-1}}\text{-}\text{400}{\text{cm}}^{\text{-1}}$

$\overline{\text{ν}}=\frac{\text{1}}{\text{λ}}\boxed{\text{λ}=wavelength}$

• Wavenumber increases with increase in frequency.

(b)

Interpretation Introduction

Interpretation:

The wavelengths which represents bending and stretching vibrations has to be determined.

Concept introduction:

• Electromagnetic spectrum is a range of all types of electromagnetic radiation.

• IR Spectroscopy: The bonds between atoms in the molecule stretch and bend, absorbing IR energy and creating the IR spectrum
• Asymmetrical stretching or bending and internal rotations changes the dipole moment of a molecule. Asymmetrical stretching and bending is IR active. Symmetrical stretching and bending does not change the dipole moment of a molecule and so it is not IR active.
• Vibrations in a Non-linear triatomic ($H_{2}O$) molecule is shown below,

• IR spectroscopy is used to identify the functional groups in a compound. The frequencies in IR spectroscopy are reported using a unit called wavenumber and it is represented by $\overline{\nu }$ and their unit is $c{m}^{-1}$ . using wavenumber scale, IR absorptions occurs from $\text{4000}{\text{cm}}^{\text{-1}}\text{-}\text{400}{\text{cm}}^{\text{-1}}$

$\overline{\text{ν}}=\frac{\text{1}}{\text{λ}}\boxed{\text{λ}=wavelength}$

• Wavenumber increases with increase in frequency.
• $\text{C}=\text{νλ}\boxed{\begin{array}{l}C\text{-}\text{speed}\text{of}\text{the}\text{light}\\ \text{ν}\text{-}\text{frequency}\\ \text{λ}\text{-}\text{wavelength}\end{array}}$
• Less amount of energy is needed to bend a molecule than to stretch it.