Classification Monosaccharides Chiral Carbon Atoms

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					  Carbohydrates
     Classification
   Monosaccharides
 Chiral Carbon Atoms
Structures of Important
    Monosaccharides
   Cyclic Structures
                          1
          Carbohydrates

• Major source of energy from our diet

• Composed of the elements C, H and
 O

• Produced by photosynthesis in
 plants
                                         2
   Types of Carbohydrates
• Monosacchrides

• Disaccharides
     Contain 2 monosacchride units

• Polysacchrides
    Contain many monosacchride units
                                       3
        Monosacchrides
• Three Carbons =   Triose

• Four Carbons =    Tetrose

• Five Carbons =    Pentose

• Six Carbons =     Hexose
                              4
        Monosacchrides
• Aldoses are monosacchrides with an
  aldehyde group and many hydroxyl (-OH)
  groups.

• Ketoses are monosacchrides with a
  ketone group and many hydroxyl (-OH)
  groups.


                                           5
      Learning Check C1
Identify each as tetrose, pentose or
hexose, and as aldose or ketose
  H
      C O                     CH2OH
  H C OH
                              C O
  H C OH
                         HO C H
  H C OH
                           H C OH
  H C OH
                              CH2OH
      CH2OH
      A                         B      6
              Solution C1
    H
        C O
                         CH2OH
    H C OH
                         C O
    H C OH
    H C OH           HO C H

    H C OH            H C OH
        CH2OH            CH2OH

        A                   B
aldose, hexose       ketose, pentose
                                       7
           Chiral Objects
• Chiral compounds have the same number
  of atoms arranged differently in space.
• A chiral carbon atom has four different
  groups attached




                                        8
             Mirror Images
• The three-dimensional structure of a chiral
  compound has a mirror image.
• Your hands are chiral. Try to superimpose
  your thumbs, palms, back of hands, and little
  fingers. Is it possible? Why or why not?




                                            9
Tetrahedral
carbon atom
bonded to four
different groups




                   10
ARE THERE CHIRAL C-ATOMS
  IN THESE MOLECULES?
      CH3CHClCH2CH3
           A

        CH2ClCH3
           B

                       11
        Learning Check C2
Determine if there is a chiral carbon in
each compound.
     Cl                        Cl
H       C CH 3          H       C CH3
        CH 2 CH 3               H
    A                           B
                                           12
              Solution C2
       Cl                       Cl
H      C CH3               H    C CH3
       CH2CH3                   H
A Yes, 4 different             B No, the
    groups are attached          2 H atoms
    to the second C atom         are identical
                                           13
14
Glyceraldehyde




                 15
         D and L Notation
• D,L tells which of the two chiral isomers
  we are referring to.
• If the –OH group on the next to the bottom
  carbon atom points to the right , the
  isomer is a D-isomer; if it points left, the
  isomer is L.
• The D form is usually the isomer found in
  nature.

                                             16
      D notation

      O
H C
H C OH
H C OH
  CH2OH
            Right = D
                        17
             Glucose
 H
     C O
 H C OH
HO C H
 H C OH
 H C OH
     CH2OH


 D-Glucose
                       18
           Fructose
   CH2
     OH
   C O
HO C H
 H C OH
 H C OH
   CH2OH


 D-Fructose           19
              Galactose
  H       O
      C
 H C OH
HO C H
HO C H
 H C OH
    CH2OH
D-galactose
                          20
       Cyclic Structures
• Monosaccharides with 5-6 carbon
  atoms form cyclic structures
• The hydroxyl group on C-5 reacts
  with the aldehyde group or ketone
  group
                               O
          o


                                      21
Haworth Structure for D-Isomers
The cyclic structure of a D-isomer has
the final CH2OH group located above the
ring.
             CH2OH
                    o


                                    22
    Haworth Structure for D-
           Glucose
• Write –OH groups on the right (C2,
  C4) up
• Write –OH groups on the left (C3)
  down
• The new –OH on C1 has two
  possibilites: down for α anomer, up
  for β anomer

                                        23
Cyclization of glucose




                         24
     Haworth Structure for D-
            Glucose
     CH2OH               CH2OH
          o                   o    OH   β
     OH                  OH
OH             OH   OH
               α
          OH                  OH

α-D-Glucose               β-D-Glucose

                                            25
d-fructose




             26
              Mutarotation
• Mutarotation: A small amount of open
  chain is in equilibrium with the cyclic
  forms.
• The most stable form of glucose is β-D-
  glucose .

α-D-glucose   D-glucose (open)   β-D-glucose
(36%)            (trace)            (64%)
                                            27
      Learning Check C3
Write the cyclic form of α-D-galactose
               H       O
                   C
              H C OH
            HO C H
            HO C H
              H C OH
                   CH2OH                 28
Solution C3

     CH2OH

OH        o
     OH
               OH

          OH
α-D-galactose
                    29