Forensic Applications of IR spec

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Forensic Applications of IR spec
2010-10-23 15:35:47
BU Forensic Chem

BU Forensic Chem Lecture 3.2
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  1. The _____ energy side of the visible spectrum is called the infrared (IR) region.
  2. How is IR similar to UV-Vis?
    IR spectrometers permit the absorption spectra of compounds to be determined.
  3. T/F: Photon energies within the infrared region are not large enough to affect the electron transitions to higher energy levels.
  4. IR spectroscopy can provide ____________ identification of samples.
    unambiguous or qualitative
  5. Why is the x-axis not liner in an infrared spectra?
    the x-axis represents the number of wave cycles in one centimeter
  6. How do you calculate the degrees of vibrational freedom?

    6 is the number of molecular translations and rotations

    n is the number of atoms in the molecule
  7. The exact frequency at which a vibration occurs is determined by what three factors?
    • 1) the strengths of the bonds involved
    • 2) the mass of the component atoms
    • 3) the type of molecular vibration
  8. What are the types of vibrational modes?
    • stretching
    • bending
    • scissoring
    • rocking
    • twisting
  9. T/F: IR spectra can be only be obtained in the solid phases.
    False! It can be obtained in all phases; liquid, gas, and solid!
  10. 4000-1000 cm-1 is known as what region of an IR spectra?
    functional group region
  11. <1000 cm-1 is known as what region of an IR spectra?
    fingerprint region
  12. In what region is most of the information used to interpret an IR spectrum located?
    functional group region
  13. T/F: In practice, it is the non-polar covalent bonds that are IR "active" and whose excitation can be observed in an IR spectrum.
    False! It is the poler covalent bonds that are IR active.
  14. T/F: It is useful to assign every peak in an IR spectrum.
    False! You should avoid this temptation