Hints on Column Chromatography

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Lecture 5
HDI More Sample Problems (NMR
IR) Due Lecture Problem 3
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HDI A Tool for Unknown Determination

• When given an unknowns MF, determine the HDI
  (hydrogen deficiency index).
• HDI
• Write out the MF of the corresponding alkane
  (CnH2n2)
• Subtract the given unknown MF from the alkane MF
• If there is a nitrogen (N) in the MF, remove an
  NH before the
• subtraction.
• Disregard an oxygen if it appears in the
  unknowns MF
• If theres a halogen, replace the halogen with
  an H

• 3. Divide the number by 2 to give you HDI.
• Example Determine the HDI of a compound whose
  MF is C8H16.
• C8H18
• C8H16
• 2 Thus, HDI 2/2 1
• This means that there may be a ring or a double
  bond in the molecule.

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HDI Some Possibilities

• HDI 1
• One double bond
• One ring
• HDI 2
• One triple bond
• One double bond, one ring
• HDI 3
• One triple bond, one ring
• One triple bond, one double bond
• Two double bonds, one ring
• Three rings
• HDI 4
• Four double bonds
• Two triple bonds
• One triple bond, two double bonds
• A benzene (phenyl) ring

Each p bond has an HDI of 1. Each ring has an HDI
of 1.

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Solving Spectral Unknown Problems

• Determine HDI if MF is given. If not given,
  then use mass spec data.
• 2. Evaluate the IR spectrums functional group
  region. Use correlation
• chart.
• 3. Evaluate the 1H NMR
• Count the of signals of different types of
  Hs
• Look at the ppm values use correlation chart.
  Start by looking
• downfield (ArH, CHO, CO2H)
• c. Look at splitting patterns ? pieces of the
  molecule J values
• d. Consider the integration. If integration is
  greater than 3, must
• be symmetry

• 4. Evaluate the 13C NMR spectrum
• a. Count the of signals of different
  types of Cs
• b. Look at the ppm values use correlation
  chart. Start by looking
• downfield
• c. If DEPT info is given, determine the different
  type of carbons

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13C NMR Correlation Chart
1H NMR Correlation Chart
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IR Correlation Chart
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Sample Problem 3 Determine the structure of this
unknown (MF is C8H9Cl)
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Sample Problem 4

Propose a structure that is consistent with the
following data C7H8O (HDI 4) 1H NMR 2.43
ppm (s, 1H) 4.58 ppm (s, 2H) 7.28 ppm (m,
5H) IR 3350 cm-1
Possible compound(s)


Solution
Double check structure. Make sure splitting
patterns and ppm values make sense as well as the
integration values. Be sure that the number of
different atoms matches the MF!
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Sample Problem 5

Propose a structure that is consistent with the
following data C3H6O2 (HDI 1) 1H NMR 1.27
ppm (t, 3H) 2.66 ppm (q, 2H) 10.95 ppm (s,
1H) IR 1715 cm-1 3500-3000 cm-1
Possible compound(s)

?
?
?
Solution
Double check structure. Make sure splitting
patterns and ppm values make sense as well as
integration values. Also, make sure the numbers
and types of atoms match the MF!
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Sample Problem 6

Propose a structure that is consistent with the
following data C5H10O (HDI 1) 1H NMR 1.10
ppm (d, 6H) 2.10 ppm (s, 3H) 2.50 ppm (m,
1H) IR 1720 cm-1

?
Solution
Double check structure. Make sure splitting
patterns and ppm values make sense as well as
integration values. Also, make sure the numbers
and types of atoms match the MF!
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Sample Problem 7
Handout given in class.