Organic Reactions

1
Organic Reactions

• Kinds of Reactions
• Mechanisms (polar, non-polar)
• Bond Dissociation Energy
• Reaction Profiles

2
Types of Reactions

• Addition Reactions
• Elimination Reactions

3
Types of Reactions

• Substitution
• Polar
• Non-polar

4
Rearrangement
5
(No Transcript)
6
Definitions

• Mechanism Complete step-by-step of exactly which
  bonds break and which bonds form and in what
  order.
• Thermodynamics The study of the energy changes
  that occur in chemical transformations. This
  allows for comparison of stability of reactants
  and products.
• Kinetics The study of reaction rates,
  determining which products are formed most
  rapidly. One can predict how the rate will
  change with changing conditions.

7
Reaction Profile (Exothermic)
8
2nd Order Reaction
9
1st Order Reaction
10
Bond BreakingNon-polar and Polar
11
Bond FormingNon-polar and Polar
12
Non-polar Reaction Involves Free Radicals
13
Free Radicals are Neutral, but Electron-Deficient
14
Free Radical Chlorination
15
Experimental Evidence Helps to Determine Mechanism

• Chlorination does not occur at room temperature
  in the dark.
• The most effective wavelength of light is blue
  that is strongly absorbed by Cl2 gas.
• The light-initiated reaction has a high quantum
  yield (many molecules of product are formed from
  each photon of light).

16
Experimental Evidence Helps to Determine Mechanism

• Chlorination does not occur at room temperature
  in the dark.
• The most effective wavelength of light is blue
  that is strongly absorbed by Cl2 gas.
• The light-initiated reaction has a high quantum
  yield (many molecules of product are formed from
  each photon of light).

17
Free Radical Species are Constantly Generated
Throughout the ReactionPropagation
18
Termination Reaction of any 2 Radicals
19
Enthalpy of Reaction (DHo) Measures Difference in
Strength of Bonds Broken and Bonds FormedBond
Dissociation Energy
20
DHo Sbonds broken-Sbonds formed
21
DHrxn -102 KJ/mol (McMurry)-105 KJ/mol (Wade)
22
(No Transcript)
23
Why Not This Mechanism?
24
Chlorination of Propane
25
Hs are not abstracted at the same rate.
26
Chlorination of Methylpropane
27
Tertiary Hs removed five times more readily than
primary Hs in chlorination reactions
28
3o Radicals are Easiest to Form
29
Stability of Free Radicals
30
(No Transcript)
31
Bromination is Very Selective
32
RDS in Bromination is highly endothermic
33
Consider the free radical monochlorination of
2,2,5-trimethylhexane. Draw all of the unique
products (ignore stereoisomers use zig-zag
structures please) and predict the ratio or
percent composition of the products.The relative
reactivity of H abstraction in a chlorination
reaction 1o 2o 3o 1 4.5 5.5
34
Chlorofluorocarbons and the Depletion of Ozone
35
Polar ReactionsNucleophiles Electrophiles
36
(No Transcript)
37
Nucleophiles are BasesElectrophiles are Acids
38
Addition of HBr to Ethylene
39
DGo DHo - TDSo
40
(No Transcript)
41
(No Transcript)
42
Reactions Often Go Through Intermediates
43
Transition State
44
(No Transcript)
45
Addition Reaction is a Two-Step Mechanism
46
(No Transcript)
47
How Many Mechanistic Steps?How Many
Intermediates?How Many Transition States?Which
Step is Rate-Determining?