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TYPES OF ORGANIC CHEMICAL REACTIONS - PowerPoint

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									 TYPES OF ORGANIC
CHEMICAL REACTIONS
     Categories of Simple Organic
              Reactions
•   Substitution
•   Addition
•   Condensation/elimination
•   Hydrolysis
•   Mild oxidation & strong oxidation
•   Combustion
•   Acid/base reactions
      Substitution Reactions
A substitution reaction occurs whenever one
  atom of an organic molecule is replaced
  by another.
Substitution reactions often require heat
  and/or a catalyst in order to occur.
Example: Substitution of an alkane
     H                         H
                      
  H C H + Cl2   H C Cl + HCl
                    HEAT

     H                        H
     Substitution of Benzene
Due to the strong bonding arrangement between the carbon atoms
in a benzene ring, the ring cannot be easily broken during
chemical changes. The hydrogen atoms that are bonded to each
carbon can be substituted for other atoms and groups.
Examples:
      H                                         Br


            + Br2       
                     
                       FeBr 3..catalyst              +   HBr




            + HNO3   H 2 SO 4              NO2 +     H 2O

            TNT synthesis…
           Addition Reactions
• In addition reactions, new atoms or groups are
  bonded to the atoms of an organic molecule.
  The organic molecule must be unsaturated to
  start with (double or triple bonds!)
                         I’m now ready
• New bonds can be made to the carbon atoms
                         to make more
  involved in the double or triple bond if the  part
                         bonds!
  of the bond is first broken.

                                 H      H

 CH2=CH2    
               breakpibond      C      C
                                 H      H
    Some Simple Addition Reactions
H         H                   H H
    C=C           + H2     H-C-C-H   (a.k.a. “hydrogenation”)
H         H                   HH


H             H             H H
        C=C       + HCl  H-C-C-Cl
H             H             HH

    H         H               H H
        C=C       + H2O    H-C-C-OH (a.k.a. “hydrolysis”)
H             H               HH
        Testing for unsaturated
             hydrocarbons
• Unsaturated hydrocarbons can be
  identified by their reaction with aqueous
  bromine, Br2(aq).
Demo! H       H               H H
           C=C       + Br2    Br-C-C-Br
       H         H               HH
           (deep orange)      (colourless)

   Completely saturated molecules DO NOT react
   in this manner- thus the orange colour remains.
          Markovnikov’s Rule
• If the double or triple bond is part of a molecule
  with three or more carbon atoms in the chain,
  the most likely addition reaction products can be
  predicted using a rule first formulated by the
  Russian chemist V.V. Markovnikov.
                Markovnikov’s Rule
…the more electronegative atom will
  predominantly bond to the carbon atom of
  the double bond that has fewer hydrogen
  atoms.
Eg.1        Markovnikov’s Rule
H                                     H OH
  C=C-CH3     + H2O 
                                   H- C - C- CH3
H    H
                                      H H

                   It should be mentioned that the primary
                   alcohol (1-propanol) is also a possibility, but
                   it would be produced in a much lower
                   proportion than the 2-propanol shown
Eg.2               above.

                                         H   Cl
 H-C  C-CH2-CH3     + 2HCl           H-C - C-CH2-CH3
                                         H Cl
       Most favoured product!
        Condensation/Elimination
              Reactions
 • Organic compounds containing hydroxyl or
   carboxyl groups can combine by eliminating a
   molecule of water between them.

                                   An ether is created!
Example 1- condensation of two alcohols

  H H                     H H          H H H H
H-C - C-O-H                       H-C - C-O-C–C-H
               + H-O-C - C-H H 2 SO4
  H H                     H H          H H    H H
       Molecule of H O is formed              +   H2O
                2
      Condensation/elimination
• When an alcohol reacts with a carboxylic acid to
  eliminate a molecule of water between them, the
  resulting bond creates an ester linkage as
  shown below:
                                 We’ve created an ester

  H H             O
H-C - C-O-H + H-O-C – CH2-CH3                 O
  H H                     If excess -CH2- O- C-CH2-CH3
                                 CH2 water is
                          added to an ester, the
                                           +
                          reaction will reverse
                          itself.         H2O
                   Uses of Esters
                             Demo!
• Esters often have characteristic flavours and
  aromas which allows them to be used in food
  products.
•   Methanol + butanoic acid  methyl butanoate (apples)
•   Octanol + acetic acid  octyl acetate (orange)
•   Benzyl alcohol + butanoic acid  phenyl butanoate (flowers)
•   Pentanol + acetic acid  pentyl acetate
     Condensation/elimination
• If a molecule of water is eliminated from within a
  single molecule, an unsaturated compound is
  formed and the molecule is said to be
  “dehydrated.”
        H                            H
    H

                   OH                          H
               H        
                        H 2 SO 4

                                             + H2O
         Oxidation Reactions
• In the terminology of organic chemistry, when a
  molecule is oxidized, the number bonds to oxygen
  atoms increases within the molecule.
• Oxidizing agents are varied: CrO3/H+, KMnO4,
  K2Cr2O7
• Often, the oxidizing agent is represented simply
  as “O” over the reaction arrow:


                  
                    O
             Oxidation Reactions
Mild Oxidation
            ..O
1o alcohol mild aldehyde
    H                  O
              
CH3-C-OH   CH3-C-H
          mild ..O


    H
 ethanol           ethanal
Strong Oxidation
1o alcohol     
               Carboxylic acid
              strong ..O

    H                          O
CH3-C-OH       
              
              strong ..O
                           CH3-C-OH
    H                      Ethanoic acid
           Oxidation Reactions
Strong Oxidation cont’d…
• Secondary alcohols require a strong oxidizing
  agent and can only be oxidized to ketones.
       OH                                      O
   CH3-C-CH2-CH3           
                          
                            strong ..O
                                           CH3-C-CH2-CH3
       H                                    butanone
     2-butanol
•Tertiary alcohols DO NOT undergo oxidation. Why not?
        OH
 CH3-C-CH3         
                  
                    strong ..O
                                         NO REACTION
     CH3
                                                       DEMOS!
   2-methyl-2-propanol
                Combustion
• All organic compounds can be combusted or
  burned. Carbon dioxide gas and water vapour
  are the products of hydrocarbon combustion.
• Combustion is really a type of very extreme
  oxidation reaction where O2(g) is the oxidizing
  agent.           BOOM!
    2C2H2(g) + 5O2(g)  4CO2(g) + 2H2O(g)


    CH3-CH2-OH(l) + 3O2(g)  2CO2(g) + 3H2O(g)
    Reactions of Organic Acids
• Like inorganic acids such as HCl(aq), organic
  acids react with bases to produce liquid water
  and a salt.
Example:

            O                          O

            C-O-H                      C-O1-Na1+


                 + NaOH                    + H2O


                          Sodium benzoate
  Benzoic acid
                Time to Practice!
•   p.27 #1  3
•   p.30 #4
•   p.31 #2, 3, 5
•   p.37 #2
•   p.44 #7, 8, 9
•   p.48 #4, 5, 6
•   p.56 #6
•   p.57 #3, 4
•   p.63 #3, 5, 7, 8
•   p.68 #3, 4         Organic chemistry will get your
                       gears going!

								
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