Lecture 03, 4

• What is the study of spectroscopy focused on?

  Interaction of electromagnetic radiation with matter
• What is infrared spectroscopy primarily used for?

  Identification of organic and inorganic compounds
• How does infrared spectroscopy measure absorption?

  By measuring absorption of monochromatic radiation
• What causes absorption in infrared spectroscopy?

  Interaction between radiation and chemical bonds
• What type of information does infrared spectroscopy provide?

  Presence or absence of functional groups
• What is the range of infrared radiation in the electromagnetic spectrum?

  0.78 to 1000 mm
• How is wavelength measured in infrared spectroscopy?

  In wavenumbers (cm-1)
• What are the three sections of the infrared region?

  Near, mid, and far infrared
• What do the energies of infrared radiation correspond to?

  Covalent bond stretching and bending vibrations
• What is required for coupling of vibrations in infrared spectroscopy?

  Vibrating bonds must be joined to a central atom
• What happens to vibrational frequency with stronger bonds?

  It increases with stronger bonds
• What must occur for a molecule to absorb IR radiation?

  Net change in dipole moment upon absorption
• Why do symmetrical molecules not absorb IR radiation?

  They have no net dipole moment
• What occurs when the frequency of radiation matches the natural frequency of vibration?

  IR photon is absorbed, increasing vibration amplitude
• What is the formula for chemical dipole moment?

  μ = δd
• Can N2 gas be observed using infrared spectroscopy?

  No, it is symmetrical with no dipole moment
• Can CO2 gas be observed using infrared spectroscopy?

  Yes, it has an asymmetrical stretch
• What happens when a chemical sample is exposed to IR radiation?

  It can absorb some frequencies and transmit others
• What does the detector in IR spectroscopy measure?

  Transmitted frequencies and absorbed frequencies
• What is the role of the monochromator in an IR spectrometer?

  To separate different wavelengths of light
• What is the formula for transmittance in IR spectroscopy?

  T = I/Io
• How is transmittance often expressed?

  As a percentage (%T = I/Io x 100%)
• What are the two regions of IR spectra?

  Identification and quantification regions
• What is the fingerprint region in IR spectra?

  600 – 1200 cm-1 for compound identification
• When is IR spectroscopy preferred over UV-Vis spectroscopy?

  For identification and molecular structure analysis
• What are the applications of IR spectroscopy?

  • Identification of functional groups
  • Structure elucidation
  • Study of chemical reaction progress
  • Detection of impurities
• How is the identity of an organic compound confirmed using IR spectroscopy?

  • Match fingerprint region (600 – 1200 cm-1) with known spectrum
  • Different compounds have different fingerprint regions
  • Cannot identify enantiomers due to similar spectra
• How does IR spectroscopy help in detecting impurities?

  • Compare sample spectrum with authentic spectrum
  • Pure samples show sharp peaks
  • Impure samples show poor bands and additional peaks
• What are practical considerations when using IR spectrometers?

  Commonly double beam to correct variations
• What happens if background readings are not corrected in IR spectroscopy?

  Unwanted peaks from CO2 and H2O appear
• What materials are commonly used for sample cells in IR spectroscopy?

  NaCl and KBr windows
• What is the procedure for preparing a sample for IR spectroscopy?

  Mix analyte with dry KBr and press into a disc
• What is the limitation of IR spectroscopy regarding organic compounds?

  All organic compounds absorb infrared radiation
• What is the ATR mode in IR spectroscopy?

  Not sensitive, produces larger peaks