Introduction to Organic Reactions by yyy55749


									                               Chemistry 211                                                                          Fall 2009

                                                      Introduction to Organic Reactions
Up to now we have been exploring various aspects of organic structures and learning how to classify compounds according to functional groups present.
In the laboratory we saw some differences in acid-base behavior between amines and amides as well as alcohols and carboxylic acids. In this activity, we
will begin to explore why it is that different functional groups react differently. As with all of the other activities, there is both content and process that is
necessary to explore chemical reactivity and understand why molecules behave as they do. In this and most of the subsequent activities for the rest of the
year, we will be calling on fundamental concepts you have encountered in previous courses to help us make sense of the relationships between a
molecule’s structure and it chemical reactivity.

Learning Objectives:
1.   To classify chemical reactions according to the overall change that occurs from reactants to products.
2.   To classify chemical reactions according to the mechanism by which the reactants are transformed into the products.
3.   To simplify a difficult complex problem into a series of simpler problems that can be more easily solved.
4.   To use similarities within a series of apparently different reactions to group a large data set into several smaller data sets with common aspects so that
     each set can be studied sequentially to gain understanding of the larger data set.
                                                Introduction to Organic Reactions                                                                                                    2
   1. Suggested references: None
   2. Table 1: Examples of Organic Reactions.
               O                                           +              H       O            O       H                          O                                                                     H
                                                     H3O                                                                                                                       H2O                              O
a.                             +                                                          C
               C                       H2O                                                                         .
                                                                                                                   b              C              +    H        C         N                                       C        C   N
     CH3           CH3                                                        CH3              CH3                                      H
                                                                                               O                                                 O              -                        H    O                      O
                       O                                                                  N           H                                                             OH                                      H
     CH3               C
                                   + NH2OH
                                                                                                       + H2 O
                                                                                                                        2   CH3
                                                                                                                                  CH2            C
                                                                                                                                                      H                              CH2           C                 C
                                                                     CH3                  C                                             CH2
           CH2                 CH3                   NH3OH                                                         d.                                           H2O           CH3            CH2            CH            H
                                                                              CH2              CH3
                                                                                                                                                                                             CH3 CH2
                   O                                                                  O
     CH3                                                             CH3                                                          O                                                            O                          +
                                                                                                               +   f.
e.                 C           H + . NH3
                                   .                                                  C           -   + NH4                                                +
           CH          O                                                   CH                 O                                   C NH + H3O                                                   C            H + NH4
                                                                                                                                      2                                                             O
     CH3                                                             CH3

                   O               O                                          O                O                                  O                                                  O         O
                                                               CH3                    -         CH3                               C
                                                                                                                                                      -   OCH3
     CH3                           C           CH3                            C           C                                                     CH3                                  C         C                CH3
g.         CH2
                           CH2             O                         CH2              CH      O                         2               O                                                               O
                                   - OCH3                                             + HOCH3                                                                                                                + HOCH3
                                                                      O                                                                                   NH2                        CH3      CH2
                                                                                                           -                      O              HN                 H2 O
                                                                      C           CH2                 Cl                                                                            H2 O +          C       N
          +                                                    CH3
i.CH3 C Cl 2 CH3CH2OH                                                         O               CH3                  j.CH3          C         +
                                                                                                                                                                                               H                N
                                                                                                  +                         CH2         H                                HN
                                                                                                                                                                              NH3                           H
                                                                                          + CH3CH2OH2

                                                                                                  Is This Overwhelming??

                                                                                               How can we deal with it??
                              3                                                         Introduction to Organic Reactions
1. Background
   a. General Approach for Trying to Understand Organic Reactions.
      (1.) Basic Assumptions:
           (a.) Nature is Systematic (There are Recurring Patterns.)
           (b.) Chemical Structure and Reactivity are Related.
                Similar structural features should produce similar behavior. That is why recognizing functional groups can be useful.
      (2.) Process of Analysis: (This should sound familiar.)
           (a.) Look for Similarities and Patterns.
           (b.) Try to Group or Classify Compounds on the basis of Similarities in Structure and/or Reactivity.
           (c.) When Possible, Simplify Complex Reactions into Sequences of Simpler Steps.
           (d.) Try to Develop Theories that Correlate Behavior and Structure.
2. Similarities and Patterns: Reaction Classifications.
   a Classifications
      (1.) OVERALL RESULT:
            (a.) Fundamental Reaction Types
                 The vast majority of chemical reactions can be classified according to their overall transformation (Reactants -> Products) as Addition,
                 Elimination or Substitution reactions. Examples of these classifications are provided below:
                 Classify each reaction into one of these categories and explain how you recognized the reaction as fitting into the category.
                                      H                                         H
                              -   +        C   O                        O       C    O
                                      H                             H           H

                                           O                        O
                              -   +        C                H       C           +    Cl -
                                      H        Cl               O           H

                                      H        H                        H                        H
                                  H   N        C    O                           N            C       +
                                               H        H               H                        H
                       Introduction to Organic Reactions                                                        4
    (b.) One additional specific reaction type: Brønsted-Lowry Acid-Base Reaction
         The reaction below is classified as a Brønsted-Lowry Acid-Base Reaction. (See also Review of General Chemistry and Mathematics #
         What is the overall result of this reaction?
                             -                                        -

                                                                : :

                                                                              : :

                              : :
                              :O H
                 : :
                 O H +                                                    + H O H

         How many bonds are made and broken in this reaction?
         Presuming that the above example is characteristic of the overall reaction of a Brønsted-Lowry Acid-Base Reaction, construct a general
         definition of a Brønsted-Lowry Acid-Base Reaction.

     The REACTION MECHANISM is the sequence of reaction steps by which the structures of the reactants are rearranged as the
     reactants proceed to the products.
     • Mechanistically Simple Reactions:
        The Brønsted-Lowry Acid-Base reaction (proton transfer) shown above and below requires only 2 changes in bonding, breakage of the
        phenol O-H bond and formation of the new OH bond of water. It is reasonable to suggest the phenol O-H bond breaks as the water O-H
        forms. So the reaction probably occurs in a single reaction step.
                            -                                   : :   -

                                                                             : :
                             : :

                             :O H
                : :

                O H +                                                     + H O H

               phenol         hydroxide ion             phenoxide ion  water
        Thus, this acid-base reaction is classified as MECHANISTICALLY SIMPLE. Mechanistically simple reactions require a TOTAL of no
        more than 2 bonds broken and bonds made.
    •   Mechanistically Complex Reactions
        How many bonds are made and broken in the following reaction?

                                                          +                                 H
                                                                                       +      -
                                                        2 H2O                  H3O +       Br
                                                       !Reactants                   Products
                              5                                                       Introduction to Organic Reactions
             It is not immediately obvious as to how these bond interchanges could occur in one reaction step and there are several possible sequences of
             bond making and breaking steps that could accomplish the conversion of reactants to products. So this substitution reaction is classified as
             Mechanistically complex reactions require a TOTAL of 3 or more bonds broken and bonds made.

3. Protocol: Analysis of the Equilibrium Controlled Reactions in Table 1.
   a. Examine the reactions in Table 1 and classify each according to overall reaction as either an Addition, a Substitution, an Elimination or an
      Acid-Base reaction. Write your designations beside the reactions on page 1.
   b. Examine the reactions in Table 1 again and classify each according to Mechanism as either:
      Simple:     Involving a total of bonds made + bonds broken = 1 or 2.
      Complex: Involving a total of bonds made + bonds broken > 2.
      Again, Write your designations beside the reactions on page 1.

Reflector’s Report Discussion:
Identify the most important concepts you learned from this activity:

What questions remain?

Strategy Analyst’s Report Discussion:
Look back at the process used to divide the overwhelming set of reactions into subsets with common characteristics. There were two bases used to
subdivide the reactions.
What insights did your group have about the reactions from the Reaction Type classification?

What insights did your group have about the reactions from the Mechanism classification?

Which subgroup might be the best place to start in trying to understand how and why these reactions occur as they do? Explain.
                                     Introduction to Organic Reactions                          6
Out of Class Applications:
A. Reading assignment in CGWW: none.
B. Activity
   1. Classify each of the following reactions:
      a. As an addition, elimination, substitution or acid-base reaction. Explain your logic.
      b. As either a simple or complex reaction. Explain your logic.

               H Br          +


                                 +   . NH3
                                                          -   +        +
                       I                              I               NH4

                                                                       +               -
                   C       CH2 + H      Cl                            C     CH3 + Cl

       (4.)                 Br                           +
              CH3 NH2 +          C                   CH3 NH2 C

C. Appropriate Problems in CGWW: none

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