spectroscopy chemistry

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ghoran
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292478
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spectroscopy chemistry
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2015-01-06 05:00:47
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  1. fingerprint region
    area on the IR spectrum below 1500cm-1
  2. fingerprint region can be used to identify
    a molecule because it's unique for a particular molecule so gives an exact match on a computer database
  3. what peaks are wide
    OH
  4. what peaks are strong and sharp
    C=O (aldehyde)
  5. carboxylic acid peaks
    • broad at OH 
    • strong and sharp at C=O
  6. ester peaks
    • strong and sharp at C=O 
    • C-O absorptions x 2 at different frequencies between range
  7. mass spec stages 
    ionization , acceleration , deflection , detection 
  8. ionisation 
    high energy electrons from an electron gun remove an electron from the outer shell of atoms in the sample 
  9. acceleration 
    positive ions accelerated towards negatively charged plate by magnetic field 
  10. deflection 
    ions are deflected according to their mz ratio by a magnetic field 
  11. detection 
    ions hit the detector and pick up electrons this produces a current proportional to the number of ions 
  12. molecular ion is 
    • an ionized molecule corresponding to MR of the molecule
    • the peak with the highest mz value 
  13. base peak 
    tallest most stable peak 
  14. fragmentation 
    breaking of covalent bonds within the ionized molecule 
  15. X+* --> 
    Y+ Z*
  16. ketone fragments give a 
    stable ion RCO+ this is because the the ion has a positive charge localized on the C atom and the carbonyl group is polarized 
  17. a small peak may appear on a mass spectrum with m/z value one unit greater than that of the molecular ion due to 
    the presence of a carbon 13 isotope 
  18. why does CH3Cl have two peaks 
    because Cl has two isotopes Cl35 and Cl37 therefor molecular ion peaks m/z 50 and m/z 52 
  19. which carbon has the highest chemical shift
    the second because electrongative O withdraws electrons and deshields carbon causing it experience greater magnetic field and resonate at higher frequency 
  20. how many peaks on proton NMR and CNMR 
    • NMR - 2 
    • CNMR - 2 
  21. how many peaks on CNMR 
    3
  22. HOW many peaks NMR
    which peak has highest chemical shift 
    • 3 peaks 
    • OH peak the H in this peak is the closest H to electrongative O 
  23. NMR can detect H and C due to 
    • unequal numbers of proton/neutron in nucleus
    • the environment of H creates different peaks and hence can be used to identify chemicals 
  24. number of peaks in NMR tells us 
    the number of different hydrogen environments 
  25. integration value tells us 
    how many hydrogens are in a particular environment 
  26. chemical shift tells us 
    what atoms/functional groups the H's are attached to 
  27. the more electronegative the group the h is attached to or near to 
    the greater the delta chemical shift value
  28. the splitting pattern tells us 
    • how many h's are next to the group (n+1 value)
    • cannot split more than 3 bonds away 
  29. common triplet quartet 
    CH3CH2
  30. common triplet triplet
    CH2CH2
  31. common singlet with integration 9 
    • (CH3)3
  32. reference 
    • TMS
    • (CH3)4Si 
  33. why is TMS a good reference 
    • inert and non toxic 
    • single and intense peak (12 equivalent protons)
    • low bp so easy to remove 
    • low electronegativity of Si so all other molecules will appear downfield 
  34. solvents 
    • CCl4
    • CDCl3
  35. why can water not be used as a solvent 
    because it contains protons which would produce a peak in the spectrum 
  36. common doublet quartet 
    CH3CH 
  37. alkene + bromine 
    = alkane 
  38. to get geometrical isomerism 
    you must have two different groups on the left of the bond and two different groups on the right hand end . it doesn't matter if the left hand groups are the same as the right hand groups or not 
  39. if a substance is added to water and there are no misty fumes we known we must not be dealing with an
    acyl chloride 
  40. mobile phase 
    carries the soluble components of the chromatography mixture that are attracted to it 
  41. stationary phase 
    retains the components of the chromatography mixture that are attracted to it 
  42. column chromatography mobile phase 
    suitable solvent 
  43. column chromatography stationary phase 
    silica/Al2O3
  44. how do we separate amino acids 
    column chromatography 
  45. advantage of column chromatography 
    separates and collects a large amount of mixture 
  46. gas liquid chromatography mobile phase 
    nitrogen 
  47. gas liquid chromatography stationary phase 
    powder coated with oil 
  48. retention time 
    time taken for compound to travel through column 
  49. most soluble compounds have a ...
    retention time 
  50. on GC chromatogram the area under each peak is proportional to 
    the amount of substance 
  51. components may be identified using a GC by 
    being fed directly into IR mass spectrometer or NMR spectroscopy 
  52. gas liquid chromatography can be used for 
    testing athletes urine or for blood samples for drugs 
  53. column chromatography 
    mixture washed through column components separate out according to how soluble they are in the mobile phase and how strongly they are absorbed onto the stationary phase . Each component will spend time absorbed onto the stationary phase and dissolved in the mobile phase . The longer the time spent dissolved on the mobile phase (i.e. the more soluble the component) the quicker it travels down the column , the smaller the retention time 
  54. volatile 
    not very soluble 
  55. why is column chromatography able to separate a mixture of components 
    • mobile phase = solvent (carries the soluble components of the chromatography mixture that are attracted to it ) 
    • stationary phase = silica (retains the components of the chromatography mixture that are attracted to it) 
    • separation depends on balance between solubility or affinity (of compounds) in each phase
  56. What two properties of the ions determine how much they are deflected by the magnetic
    field? What effect does each of these properties have on the amount of deflection? 
    • Mass and charge. The heavier the ion, the less it is deflected. The higher the positive
    • charge, the more it is deflected. 
  57. Of the three different ion streams in the diagram above, why is the red one least
    deflected?
    • Assuming that all of the ion streams have the same charge, then this must have the
    • heaviest ions. To be more general about it, the least deflected ion stream will be the one with the
    • highest mass/charge ratio.
  58. What would you have to do to focus the red stream on the detector?
    You would need to increase the magnetic field.
  59. Why is it important that there is a vacuum in the instrument?
    to avoid the possibility of the ions hitting, and being deflected by, air molecules.

  60. Explain as fully as possible what the mass spectrum shows about zirconium
    • Zirconium has 5 isotopes with relative isotopic masses of 90, 91, 92, 94 and 96.
    • The most abundant one is Zr-90, followed by Zr-94 and Zr-92 which have similar abundances.Then Zr-91, and the least abundant is Zr-96
  61. The spectrum shows lines for 1+ ions. If there were also peaks for 2+ ions, where would you
    expect to find them, and what would you predict about their heights relative to the 1+ peaks?
    • You would find a similar set of peaks but at exactly half the m/z values. The heights of the peaks
    • are likely to be much less than the corresponding ones with 1+ ions, because a 2+ ion is less likelyto form than a 1+ ion.

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