Infrared spectroscopy

• What s an infrared spectroscopy?

  a technique that can be used to identify the bonds

  present in a molecule.
• What can covalent bonds absorb?

  infrared radiation which causes them to bend stretch and vibrate - all bonds have their own characteristic absorptions
• How is infrared spectroscopy used to identify different functional groups in organic compounds?

  1) A beam of infrared radiation is passed through the sample chemical2) Bonds between different atoms absorb different frequencies of IR3) IR causes covalent bonds to vibrate more4) IR that is not absorbed is detected by a detector
• What are the axis of the infrared spectrum?

  y axis = transmittance

  x axis = wavenumber nm-1
• What is the fingerprint region?

  Area of the infrared spectrum below wavenumber of 1500cm-1

  Many peaks, caused by complex vibrations of the whole molecule. Usually things like C-C, C-X, C-F, C-O
• Which bond should you not get confused about and why?

  - O-H bond is not to be confused- As it could be the OH bond of analcoholor acarboxylic acid
• How can you physically identify an alcohol on IR spectomteter

  Smooth tongue
• How can you physically identify a carboxlyic acid on IR spectomteter

  BROAD beard
• What kind of gases can absorb IR and why?

  Atmospheric gases can absorb IR

  This is because of covalent bonds such as: C=O, C-H and O-H which are present
• What does the IR absoprtion of atmopheric gases lead to?

  Global warming
• Is water a greenhouse gas? What is it's characteristic bond?

  YES if it has the (g) symbol - AKA steam

  C=O is its characteristic bond
• Explain how infrared absorbed by greenhouse gases (5)

  - Earth receives most of its energy from the sun in form of visible light

  
  

  - Some light reflected, but remainder of incoming radiation passes unchanged through the atmosphere to reach the

  earth's surface.

  
  

  - Greenhouse gases in the atmosphere do not absorb energy in this region of the

  spectrum.

  
  

  - The surface of the earth is warmed, and re-emits energy in the INFRARED REGION

  
  

  - Most of this re-emitted energy returns to space but the rest is

  absorbed by greenhouse gases in the atmosphere.
• Give One important application of infrared spectroscopy? And explain how it works

  - involves measuring the

  amount of ethanol in the breath of suspected drunken drivers using a breathalyzer.

  
  

  - Measures intensity of O-H and C-O absorption peaks and sees if it goes over legal amount
• What can mass spectrometry be used for?

  - find theabundanceandmassof each isotope in an element allowing us todetermine its relative atomic mass

  - find Mr of substance made of molecules

  - Identify organic compounds by gaining structural information about them.
• Give three applications of mass spectometry

  - Monitoring levels of environmental pollution such as lead.

  - Drug testing in sport.

  - Space probes visiting Mars carry mass spectrometers to identify elements in

  rock samples.
• How does mass spectrometer work?

  - spectrometer ionizes the sample under investigation, and then determines the mass-to-charge ratio (or m/z) of the positive ions present.

  -(M/z = mr)

  - Graph with percentage abundance (=y-axis) and the m/z (=x-axis) is represented

  - This info can be substituted in Ar abundance equation
• How can a mass spectrometer be used to identify organic olecules? Explain how?

  - In a mass spectrometer, organic moleculeslose an electronto form a1+ ion.- positive ion is called themolecular ion peak or the M+ion.-
• What is the M+ peak in mass spec?

  Highest peak on right of mass spec

  
  

  The peak caused by the presence of a C13 isotope
• What is the M+1 peak?

  Usually found on the right hand side of the molecular ions peak and is caused by the presence of the carbon isotope 13C

  VERY SMALL SO IGNORE - COMES AFTER M+ PEAK
• What is the m/z equivalent to? and why is this useful

  m/z = Mr of organic compound

  This tells us the Mr and therefore find the molecular ion
• How should we write the molecular ions formula of a molecule identified b the M+ peak on mass spec? and why?

  - Withsquare bracketsanda positive charge!!!

  -EG: Ethanol has been identified via a M+ peak of 46

  - Therefore we write it as[C2H5OH]+ becauseIn a mass spectrometer, organic moleculeslose an electronto form a1+ ion.
• What is fragmentation in a mass spectrometer?

  When amolecular ion breaksdown into smaller piecedfragment ion
• How can fragments be identified on a mass spec.?

  Fragments with a positive chargecause a peak in the mass spectrum.

  In which these peaks have anm/zequal to Mr of fragment ions

  Can also simply compare m/z value to table of m/z values and possible positive fragment ions
• What is one thing to ALWAYS remember about fragment ions?


  They have aPOSITIVE CHARGE!!!!!!
• FRAGMENT ION TABLE

  
• How should balanced equations showing formation of fragment ions be shown?


  Original organic compound ----> POSITIVE fragment ion + New organic compound RADICAL after having fragment removed

  
  

  (EG:

  C6H14 ----> C3H7+ + C3H7•
• How can you identify the structure of an organic positive fragment ion?

  - Examine fragmentation pattern on mass spec

  - Draw all possible structural isomers of compound

  - Eliminate certain structures comparing presence of fragment ion peaks
• What study frame can you use to identify fragment ion? (7)

  - Which of the labelled peaks is produced by the M+

  
  

  - The molecular ion (M+) peak has a m/z value of .[x]

  
  

  - Therefore the

  (Mr) of the compound is = M/Z value = [x]

  
  

  - The molecular formula of the compound is (work out)

  
  

  - Structure and name of organic molecule.

  
  

  - Draw isomers of possible isomers and see if they can form fragments

  
  

  - m/z and identity of labelled fragment ions.