Notes flashcards

• What is spectroscopy?

  Study of interaction of matter and electromagnetic radiation
• How is wavelength defined?

  Distance from one wave peak to the other, measured in nanometres
• What is wavenumber?

  Number of waves per unit length
• What is the formula for the energy of a photon?

  Energy of a photon = $\frac{hc}{\text{wavelength}}$
• What does absorption spectra indicate when an organic compound is exposed to light?

  Some energy is absorbed and some is transmitted
• What are the three ways that energy is absorbed in spectroscopy?

  • Electronic transition
  • Vibrational transition
  • Rotational transition
• Why does an organic molecule absorb some infrared (IR) light but not others?

  Because the stretching and bending are quantised
• What is stretching in the context of molecular vibrations?

  Vibration that changes the bond length
• What is bending in molecular vibrations?

  Vibration that changes bond angle
• What is a limitation of infrared spectroscopy?

  It is not sensitive as it can’t be quantified
• What information does infrared spectroscopy provide?

  It tells us the functional groups present
• When is energy absorbed in infrared spectroscopy?

  If the frequency matches the vibration
• How can a spectrum of a test drug sample be used?

  It can be compared with the spectrum of an authentic drug sample
• How can the spectrum be measured?

  • Using a liquid sample applied directly
  • Using a solid sample dispersed in KBr
• Which solvent cannot be used in infrared spectroscopy?

  Water
• Why can’t glass be used for the cells in infrared spectroscopy?

  Sunlight is absorbed and it won’t pass through
• What is a key feature of ultraviolet spectroscopy?

  It is sensitive as it can be quantified
• What type of compounds does ultraviolet spectroscopy provide information about?

  Compounds with conjugated double bonds
• What is the purpose of UV assays?

  To give drug concentration and follow biochemical reactions
• What instruments are needed to measure UV light?

  Two light sources, monochromator, sample cell, and detector
• What are the two light sources used in UV spectroscopy?

  Deuterium and tungsten lamp
• What does a monochromator do in UV spectroscopy?

  Disperses the light into different wavelengths
• What does 217 nm represent in UV spectroscopy?

  The wavelength of maximum absorption
• Why is there a spread of wavelength in UV spectroscopy?

  Due to vibrational and rotational transitions
• How does the size of the conjugated system affect wavelength absorption?

  Larger conjugated systems absorb longer wavelengths
• What is a chromophore?

  Arrangement of atoms responsible for the absorption of UV light
• What does the Beer-Lambert Law state?

  Absorbance depends on the path length and concentration of the sample
• What does C represent in the Beer-Lambert Law?

  Concentration of sample (moles/L)
• What does B represent in the Beer-Lambert Law?

  Path length in cm
• What does the molar absorptivity represent?

  It represents how strongly a chemical species absorbs light at a given wavelength