Infrared Spectroscopy: Effect on Molecules

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Questions and Answers

What types of vibrations occur in molecules when irradiated with IR radiation?

  • Rotational and translational vibrations
  • Stretching and bending vibrations (correct)
  • Symmetric and asymmetric vibrations
  • Vibrations in the UV region

In which region of the spectrum does ultraviolet radiation lie?

  • High energy side of the visible spectrum (correct)
  • Low energy side of the visible spectrum
  • Far IR region
  • Between visible and infrared spectrum

What type of energy is largely associated with infrared radiation?

  • Mechanical energy
  • Electromagnetic energy
  • Chemical energy
  • Thermal energy (correct)

What property of molecules can be determined using IR spectroscopy?

<p>Functional groups (A)</p> Signup and view all the answers

What law can be used to predict the oscillation frequency in molecules?

<p>Hooke's Law (C)</p> Signup and view all the answers

How are IR spectra usually recorded?

<p>Transmittance vs wave number (cm-1) (B)</p> Signup and view all the answers

Which factor affects the vibrational frequency of a molecule according to Hook's Law?

<p>Force constant (C)</p> Signup and view all the answers

What happens to the vibrational frequency when the bond strength of a molecule increases?

<p>Vibrational frequency increases (B)</p> Signup and view all the answers

Which type of molecules have changing or fluctuating dipole moments during vibration and are considered IR active?

<p>Molecules with heteronuclear bonds (C)</p> Signup and view all the answers

What is the formula to calculate the total degree of freedom for a linear molecule?

<p>3N - 5 (D)</p> Signup and view all the answers

Which type of molecules are considered IR inactive due to having no dipole moment?

<p>Homonuclear molecules (C)</p> Signup and view all the answers

What is the essential condition for a molecule to be IR active according to the provided text?

<p>Changing or fluctuating dipole moment during vibration (C)</p> Signup and view all the answers

Why do IR spectra appear upside down and right to left?

<p>Because of the nature of IR radiation absorption (D)</p> Signup and view all the answers

What is the essential condition for a molecule to be IR-active?

<p>Possessing a fluctuating dipole moment during vibration (A)</p> Signup and view all the answers

How many total degrees of freedom does a molecule with N atoms have?

<p>$3N$ (A)</p> Signup and view all the answers

Why are homonuclear diatomic molecules not IR-active?

<p>They do not have a fluctuating dipole moment (A)</p> Signup and view all the answers

What kind of vibrations give rise to absorption in the IR region?

<p>Vibrations that cause a fluctuating dipole moment (C)</p> Signup and view all the answers

Why do fewer bands appear in the IR spectra than theoretically possible?

<p>Because certain vibrations are not observed (B)</p> Signup and view all the answers

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