CH3 O H3C C C CH3 Cl CH2OH O O AlCl3 Br2

Chemical Reactions and Reaction Mechanisms
O
O
∆
O
H3C
C
C
CH3
O
Br
Br
C
C
Br
Br
Br2
H3C
CH3
Cl
Cl
AlCl3
CrO3, pyridine
CH2Cl2, 40°C
CH2OH
CHO
Br
Br2, hν
CCl4, 75°C
Table 6.1 has a list of common abbreviations and acronyms.
O
1) CH3Li, ethyl ether, 0°C
2) H2O
CH3
OH
CH3
CH3
95%
Organic chemical reactions fall into several basic categories:
Substitutions
OH
+ NaBr
Br
+ NaCN
H2SO4
Br
CN
O
O
C
H3C
C
+ NH3
Cl
H3C
Cl
Br
Br2, FeBr3
Addition Reactions (addition to a π-bond)
H
Br
Br2
C
H2C
BrH2C
CH3
O
1) NaCN
2) H2SO4
C
H3C
H
CH3
CH3
NC
H3C
OH
CH3
Elimination Reactions (the reverse of addition reactions)
Br
H3CO
H3CH2C
+ KOH
O
OH
CH3
C
H3CH2C
CH3
Oxidation (addition of O or removal of H)
CH2OH
O
PCC
O
KMnO4
C
C
H
OH
Reductions (addition of hydrogen)
O
NaBH4, CH3OH
C
CH2OH
O
LiAlH4, ethyl ether
C
H
OH
H
H
CO2H
H
CO2H
H2, Pd/C
H
H
SCH3
H
H
H
H
H2, Raney Ni
Rearrangements and Pericyclic Reactions
O
O
∆
Cl
H
O
AlCl3
Cl
O
O
C
C
OCH3
O
OCH3
Practice
H3C
H3C
C
CH3OH
Br
H3C
H3C
H3C
C
OCH3
H3C
O
H3COH2C
H3COH2C
1) CH3LI
2) H2O
O
O
O
HO CH
3
H
CH3
H
MCPBA
H3C
O
CH3
H3C
H
H
H
CH3
HBr
H3C
CH3CH2CHBrCH3
H
NO2
HNO3/H2SO4
OH
PBr3
Br
CN
CH2NH2
LiAlH4
Cl
O
Cl
AlCl3
O
O
Reactions...
Polar
Homolytic (Radical)
Pericyclic
In polar reactions, the reactants can be classified as...
electrophiles
or nucleophiles.
Electrophiles
H3C
C
CH3
H3C
Nucleophiles
F
B
F
Br
F
C
H3C
Li
H3C
H
O
H
H3C
CH3
N
H
H3C
H3C
Cl
H
O
O
C
H
H
H
H
C
P
Cl
CH3
C
H3C
H
H3C
C
N
C
CH3
MgBr
Reaction Mechanisms A quick review of what we need to know of kinetics.
An elementary process...
H
H
C
NC
H
NC
Br
C
H
H
Br
H
Molecularity...
A reaction mechanism...
H3C
H3C
C
O
H
H3C
H3C
H3C
C
OH2
H3C
H
C
O
H
CH3
Br
H3C
An intermediate...
A catalyst...
The rate determining step...
The rate law or rate
equation...
The order of reaction...
CH3
O
H
H3C
H
C
O
H
H3C
H3C
O
H3C
H
H3C
H3C
C
H
H3C
H3C
C
H3C
Br
H
H
Arrows
Organic chemists use arrows to indicate the flow of electrons in a mechanism. The
importance of this formalism cannot be overstated.
ARROWS ALWAYS START AT ELECTRON PAIRS (either lone pairs or bonds)
AND NEVER INDICATE THE MOVEMENT OF AN ATOM.
CH3
H3C
N
C
O
C
C
NC
H3C
O
H3C
Pericyclic reactions are "concerted"...
In radical reactions, half-arrows are used to show the movement of single electrons.
H
H
Br
Br
H
H
Practice...
H3C
H3C
C
H3C
H
O
H
H3C
Br
H3C
O
H
C
C
CH3
CH3
H3CS
C
H3C
O
H
H
H3CS
OH
CN
O
CN
O
O
H
OH
H
H
H
H
H
C
C
CH3
H
H
H3C
H3C
H3C
C
Br
FeBr3
Br
Br
FeBr3
Br
H
NH2
H
H
O
H
OCH3
CH3
H3C
H3C
H
O
NH2
C
H
Br
C
CH3
CH3
H
C
H
H3C
H
Br
H
Br
C
H3C
H
Br
CH3
C
H3C
H
C
C
C
H
C
H
H
C
H3C
H
Organic Acid/Base
Chemistry
You will recall (I love saying that…) that for the generic acid, HA:
+ ][ A− ]
[
H
Ka =
[ HA]
Organic chemists typically refer to pK a rather than Ka .
pK a = − log[ K a ]
This is just like pH. Remember, the lower the pH, the higher the [H+ ]. In using pK as,
strong acids (large Kas) have
while weak acids (low Kas) have
Some typical pKas
HClO 4 -1 0
HF
3 .1
NH 4 9 .2
H2 O
1 5 .7
H2
35
Important Trends in Acidity
Across the period…
Acid
Conj. Base
H3 C
H
H2 N
H
HO
H
F
pKa
H
Down a group…
HO
H
15 .7
HS
H
11
Hybridization…
H3 C
H
48
H
C
45
H
C
H
25
H
O
H
O
H
-2
-4 to-1 0
Resonance…
H3 C
CH 2
17
O
H
O
H3 C
C
O
4.7 2
H
O
H
10
Resonance effects greatly enhance the acidity of “activated” C—H bonds.
O
H
CH 2
1 9 -2 5
H
N
C
C
H2
25
O
O
H
9-1 4
H
Inductive
and Field Effects…
O
X
C
C
H2
OH
X=
p Ka
CH 3
H
I
Br
Cl
F
CN
NO 2
4.8 7
4.7 6
3.1 7
2.9 0
2.8 6
2.5 9
2.4 6
1.6 8
These effects are
ClH 2 C
O
O
C
C
OH
O
C
Cl2 HC
2 .8 5
OH
Cl 3 C
1 .4 8
OH
0 .7 0
These effects
O
O
C
4 .8 2
C
OH
Cl
C
OH
Cl 2 .8 6
4 .0 5
O
O
C
Cl
OH
4 .5 2
OH
Lewis Acid/Base Reactions
F
F
F
O
B
C2H5
F
O
C2H5
F
H3C
CH3
H3C
B
C2H5
F
C2H5
Br
C
H3C
CH3
C
Br
H3C
Amphiprotic species
CH3OH + H2SO4
H
CH3OH +
N
H
Acids and Bases/Electophiles and Nucleophiles
O
H3C
H
HO
Br
H+
H
H2O
O
O
C
C
H3C
CH3
CH3
H3C
H+
H
O
H2O
O
C
H3C
CH3
C
H3C
CH3
CH3
Br
In Organic Chemistry, it is very important to generalize.
H3C
OH
CH3CH2
OH
CH3CH2CH2
OH
HI
H3C
HI
I
CH3CH2
HI
CH3CH2CH2
I
I
This is a general method for the preparation of alkyl iodides from(1°) alcohols.
R
OH
HI
R
I
To be an effective organic chemist, you must be able to recognize reactants, solvents,
reaction conditions (such as temperature, uv light, etc.).
You must be able to recognize the stereochemical implications of the reactions you use
in the context of the reactant structure.
You must be able to classify your reactants and understand their actual structure.
Reaction Profile Diagrams follow the change in energy during a collision.
1)
NC
2)
NC
3)
S
H
H
S
H
H
NC
NC
4)
H
S
H
H
S
NC H
5)
H
S
H
3
4
2
"E"
1
5
RC
HBr
O
H
H3C
H3C
CH3
CH3
Br
Br
H
O
O
C
C
CH3
Br
C
C
H3C
HO
H3C
HO
Br
C
CH3
H3C
CH3

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