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Flashcards

Structure Determination

julia_reast_93 Organic Chem University Inglês 42 flashcards

Structure Determination

Flashcards do conjunto (42)

  1. 1how do you calculate empirical formula?Step 1: divide % abundance by atomic weight
    Step 2: Divide each value from Step 1 by the lowest value
  2. 2How do you obtain the molecular formula?Step 1: calculate the molecular weight of the empirical formula
    Step 2: Obtain the molecular weight from data given/ mass spectrum
    Step 3: divide molecular weight of sample by molecular weight of empirical formula
    -the number from step 3 is how many times the empirical formula fits into molecular formula
  3. 3Alternative method to calculate molecular formulaStep 1: convert % abundance of element in to a decimal
    Step 2: put it into the following eqn
    no.of atoms = (decimal*molecular mass)/atomic mass
    Step 3: repeat for all other elements in the sample
  4. 4How do you find the number of double bond equivalents?Step 1: Imagine a linear chain of the C, N and O atoms and work out how many Hs required to give a fully saturated molecule.
    Step 2: Compare the no. of H atoms needed so that the molecule is saturated. Half of the difference in these numbers is the number of double bond equivalents
  5. 51 DBE1 double bond/1 ring
  6. 62 DBE2 double bonds
    1 double bond + 1 ring
    2 rings
    1 triple bond
  7. 74 DBE special casecan be a benzene ring
  8. 8Beer-Lambert LawA=εlc
  9. 9IR 600-1400 cm-1Fingerprint region
  10. 10IR 1600- 1850 cm-1C=C
    C=O
    C=N
  11. 11IR 2100-2300 cm-1triple bonds
    CC
    CN
  12. 12IR 2700-3000 cm-1C-H
  13. 13IR 3000-3200 cm-1O-H
  14. 14IR 3200-3450 cm-1N-H
  15. 15H NMR δ7-δ8Aromatic protons
  16. 16H NMR δ5-δ6Vinyl Protons
    C=C-H
  17. 17H NMR δ2.5Acetylenic protons
    R-C-C-H
  18. 18H NMR δ9-δ10Aldehyde proton
    O-C(R)-H
  19. 19H NMR δ10+Carboxylic acid proton
  20. 20H NMR ~δ1-2Alkane
  21. 21H NMR ~δ2.5proton attched to a triple bonded C
  22. 22C NMR δ165-210C=O
  23. 23C NMR δ100-150C=C
  24. 24C NMR δ65-90C-O
  25. 25C NMR δ0-40alkanes
  26. 26C NMR δ75-95C triple bonded to C
  27. 27C NMR δ110-150Aromatic
  28. 28C NMR δ30-65C-Cl
    C-BR
  29. 29H NMR Withdrawing groups next to the protonthe proton is more deshielded
  30. 30H NMR Donating groups next to HH is more shielded
  31. 31If resonance can occur such as a double bond near a carbonyl it is often the H nearest to the opposite end of the carbonyl that is more deshielded rather than the H nearest the withdrawing O because of the resonance sturucture. The same can be said for the Hs near donating groups. See picsIf resonance can occur such as a double bond near a carbonyl it is often the H nearest to the opposite end of the carbonyl that is more d...
  32. 32Three factors that affect J (coupling constant)1) Dihedral angle( trans better overlap of orbitals, greater J)
    2) Bond Length (shorter bond larger J)
    3) Electronegativity (weakens communication)
  33. 33roofingwhen two portons are chemically similar their shift is much more similar and they couple slightly with each other leading to roofing where the direction of the roof points towards the other peak that is being coupled to
  34. 34—X and X' are equivalent
    They are chemically and spectrscopically identical    X and X' are equivalent They are chemically and spectrscopically identical
  35. 35—X and X' are enatiotopic.
    They are only different in a chiral environment    X and X' are enatiotopic. They are only different in a chiral environment
  36. 36—X and X' are diastereotopic
    They are always different chemically and spectroscopically, but not by predictable amounts    X and X' are diastereotopic They are always different chemically and spectroscopically, but not by predictable amounts
  37. 371H NMR exchangeDifferences in spectroscopic timescales tells us about the rates of proton exchange:
    Rate of change SLOW = two distinct signals
    Rate of change FAST = single population average is obsereved
  38. 3813C NMR Electronegative substituentsDeshield C
    Low field
  39. 39Intensity of signals in 13C NMRIn 13C, relaxation effects alter intesities of signals. Relaxation of carbon nuclei occurs via interactions with protons. Hence quaternary carbons that do not have H nearby relax very slowly and usually give weak signale
  40. 4013C-13C couplingnot usually observed unless 13C enriched molecules is synthesized
  41. 4113C-1H couplingSpectra usually recorded decoupled and so only singlets are observed
  42. 4213C-1H off resonance couplingUses weak 1H decoupling and can be used to determine the number of protons attatched to any carbon.
    Me= quartet, CH2 - triplet ect.

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University Organic Chem FlashCards sobre Structure Determination, criado por julia_reast_93 em 17-01-2014.
Criado por
julia_reast_93
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