Spectroscopy

• What is spectroscopy the study of?

  The interaction of matter and electromagnetic radiation
• What does the electromagnetic spectrum include?

  Visible light, X rays, microwaves, radio waves

  
• What are the properties of electromagnetic radiation?

  It has properties of a particle and an energy wave
• What is wavelength (λ)?

  The distance from one wave maximum to the next
• In what units is wavelength usually quoted?

  Nanometres (nm)
• What is wavenumber?

  The number of waves per unit of length
• In what units is wavenumber usually quoted?

  Reciprocal centimetres (cm−1)
• What does frequency (ν) measure?

  The number of maxima passing a fixed point per unit time
• In what units is frequency typically quoted?


  Hertz (Hz)
• What does amplitude represent in a wave?

  The height of the wave
• How can a beam of radiation act?

  Like a stream of photons
• What is the equation relating speed of light, frequency, and wavelength?


  c = νλ
• What is the formula for the energy of a photon?

  E = hc/λ
• What is Planck's constant (h)?

  6.62 x 10^-34 J.s
• What is the speed of light (c)?

  3.00 x 10⁸ m/s
• How does energy (E) vary with wavelength (λ)?

  E varies inversely with the wavelength
• What is an absorption spectrum?

  • Energy absorbed at specific wavelengths
  • Energy transmitted at other wavelengths
  • Obtained by irradiating a compound with light
• What happens when an organic compound absorbs electromagnetic radiation?

  It absorbs energy of particular wavelengths
• What can be determined from the absorption spectrum of a drug?

  Which wavelengths are absorbed and transmitted
• What are the three modes of absorption of electromagnetic radiation?

  Electronic, vibrational, and rotational transitions
• What type of light is needed for high energy transitions?

  UV or visible light
• What does 100% transmittance indicate?

  All energy is passing through the sample
• What does less than 100% transmittance indicate?

  Some energy is being absorbed
• What does each downward spike in an absorption spectrum correspond to?

  An energy absorption
• Why do organic molecules absorb some wavelengths of IR radiation?

  Stretching and bending modes are quantised
• What is stretching in infrared spectroscopy?

  A vibration changing bond length
• What happens when a molecule is irradiated by infrared radiation?

  Energy is absorbed if frequency matches vibration
• What are characteristic IR absorption bands?

  Consistent absorption bands for functional groups

  
• What is the C=C absorption wavelength?

  1660 cm^-1
• What is the C=O bond absorption wavelength?

  1700 cm^-1
• What is the O-H bond absorption wavelength?

  3450 cm^-1
• How are solid and liquid samples prepared for IR spectroscopy?

  • Liquid samples can be applied directly
  • Solid samples must be dispersed in a liquid or KBr
  • Solutions can be used with NaCl cells

  
• What type of instruments are most modern IR spectroscopy devices?

  Fourier-transform (FT) devices
• What is the function of the sample cell in UV spectroscopy?

  To place the sample for analysis
• What does the detector in UV spectroscopy do?

  It detects and measures light intensity
• What is the significance of the LUMO and HOMO in UV spectroscopy?

  They represent molecular orbitals for electron promotion

  
• What type of compounds does UV spectroscopy provide information about?

  Compounds with conjugated double bonds
• What happens when 1,3-butadiene is irradiated with UV light?

  It absorbs UV light at 217 nm

  
• What does the equation A = log I₀/I represent?

  The absorbance of a sample
• What does a larger conjugated system do to the wavelength of absorption?

  It absorbs at longer wavelengths