Understanding Organic Reactions

1
Chapter 6 Understanding Organic Reactions
2
Major Items Associated with Most Org. Rxns

• Substrate .. organic reactant being modified by
  the reagent
• 2. Reagent inorganic or organic reactant that
  modifies the substrate
• Solvent medium that dissolves the reactants

3

• Catalyst .. substance that increases rxn rate
  but retains its original structure
• Condition.. The physical or physicochemical
  quantity used in the rxn.

4
A Single Step Chemical Equation
5
Example of a Single Step Chemical Eqn.
6
Example of a Multi-step Chemical Eqn
7
Types of Reactions
(S, E, and A SEA )
8
Substitution Reactions ( Y
will replace Z at a carbon atom)
9
Substitution Reactions
10
Elimination Reactions ( X
and Y are detached from two different carbon
atoms that are vicinal to each other)
11
Elimination Reactions
12
Addition Reactions ( X and
Y add to two different atoms in a molecule that
has one or more ? bonds)
13
Addition Reactions
14
Elimination is the opposite of addition .
15
Practice Exercises Classify the following rxns as
substitution, elimination, or addition.
16
Practice Exercises Classify the following rxns as
substitution, elimination, or addition.
17
Changes in Bonding During a Chemical Rxn
(Homolysis and Heterolysis)
18
Two possible ways a bond can break
Heterolysis an unequal division of a bonding
electron pair Homolysis an equal division of
a bonding electron pair
19
Think about a simple example like H2.
20
(No Transcript)
21
Review of Using Curved Arrows in Organic
Chemistry
22
Bond breaking forms particles called reaction
intermediates.
23
Common Reaction Intermediates Formed by Breaking
a Covalent Bond
24
Practice Exercise Draw the structure of
the products for each set of reactants.
25
Practice Exercise Draw the structure of
the products for each set of reactants.
26
Bond Making
27
Thermodynamics and Bonding
28
Bond Dissociation Energy
29
Bond Dissociation Energy
30
(No Transcript)
31
Stronger bonds have a higher ?Hº
32
Calculating ?Hº Using Bond Dissociation Energy
33
(No Transcript)
34
(No Transcript)
35
Thermodynamics and Equilibrium
36
Relationship Between ?Gº and Keq
37
Relationship Between ?Gº and Keq
38
(No Transcript)
39
Free Energy, Enthalpy, and Entropy
40
Free Energy, Enthalpy, and Entropy
41
Understanding Organic Reactions
Enthalpy and Entropy
42
..when the total moles of products are the same
as the total moles of reactants
43
Using Energy Diagrams
44
Energy Diagrams
45
Drawing the Structure of the Transition State
46
(No Transcript)
47
Types of Energy Diagrams
48
Understanding Organic Reactions
Energy Diagrams
49
Energy Diagrams for Two-step Reactions
50
Energy Diagram for a Two-Step Reaction
51
Summary Notes on the Energy Diagram Ea and ?G
52
Kinetics and Rate Equations
53
(No Transcript)
54
(No Transcript)
55
(No Transcript)
56
Catalysts
57

• Catalysts
• Changes the speed of a rxn
• Does not appear in the product
• 3. Many types of catalyst can easily be
• recovered and used again

58
Identify the catalyst in each reaction
59
How do catalysts change the speed of a rxn
60
Example of an Enzyme Catalyst
61
(No Transcript)
62
Understanding Organic Reactions
Bond Making and Bond Breaking

• Homolysis generates two uncharged species with
  unpaired electrons.
• A reactive intermediate with a single unpaired
  electron is called a radical.
• Radicals are highly unstable because they contain
  an atom that does not have an octet of electrons.
• Heterolysis generates a carbocation or a
  carbanion.
• Both carbocations and carbanions are unstable
  intermediates. A carbocation contains a carbon
  surrounded by only six electrons, and a carbanion
  has a negative charge on carbon, which is not a
  very electronegative atom.

63
Understanding Organic Reactions
Writing Equations for Organic Reactions

• Equations for organic reactions are usually drawn
  with a single reaction arrow (?) between the
  starting material and product.
• The reagent, the chemical substance with which an
  organic compound reacts, is sometimes drawn on
  the left side of the equation with the other
  reactants. At other times, the reagent is drawn
  above the arrow itself.
• Although the solvent is often omitted from the
  equation, keep in mind that most organic
  reactions take place in liquid solvent.
• The solvent and temperature of the reaction may
  be added above or below the arrow.
• The symbols h? and ? are used for reactions
  that require light and heat respectively.

64
Using Arrows in Equations and Rxn Mechanisms