AROMATIC SUBSTITUTION
REACTIONS
NOMENCLATURE
Learn Nomeclature Either on Your Own
or Use the Organic Nomeclature Software
CH3
Br
methylbenzene
(toluene)
1-bromo-3-nitrobenzene
NO2
CH3
CH3
1-chloro-3-methylbenzene
Cl
CH3
1,4-dimethylbenzene
SOME SPECIAL NAMES
O CH3
CH3
NH2
toluene
aniline
anisole
CH3
CH3
CH3
OH
phenol
COOH
CH3
CH3
o-xylene
m-xylene
CH3
p-xylene
benzoic
acid
ortho, meta and para Positions
CH3
m-nitrotoluene
R
o-
m-
ipso
1
6
3-nitrotoluene
2
NO2
ortho
meta
5
1-methyl-3-nitrobenzene
Cl
3
4
p-
para
p-dichlorobenzene
Cl
1,4-dichlorobenzene
Compounds containing aromatic
rings
are often used in dyes, such as these
for
sale in a market in Nepal
Source: Getty Images
REVIEW OF BENZENE PROPERTIES
Figure 22.11: The structure of
benzene
BENZENE RESONANCE
Review Sections 6.8 - 6.14
KEKULE
STRUCTURES
Resonance Energy = 36 Kcal / mole
All bonds are equivalent
The ring is symmetric.
Bond lengths are between a single and a double bond.
Very Stable
Less reactive than other groupings of atoms.
H
.
.
.
.
H
.
H
H
.
H
H
All 2p orbitals overlap equally.
BENZENE
Isodensity surfaces - electron potential mapped in color.
(van der Waal’s)
Highest
electron density
is red.
Note the symmetry.
Color adjusted
to enhance the
pi system.
BENZENE - DETERMINATION OF RESONANCE ENERGY
cyclohexatriene
(hypothetical)
+ 3 H2
benzene
cyclohexene
+ 3 H2
RESONANCE
ENERGY
36 kcal/mol
+ H2
-49.8 kcal/mol
-28.6 kcal/mol
cyclohexane
-85.8 kcal/mol
(calculated)
REACTIVITY
The “Double Bonds” in a Benzene Ring Do Not React Like Others
Alkene
Benzene
R Cl
R
+ HCl
+ HCl
no
reaction
+ Cl2
no
reaction
+
no
reaction
H
R Cl
R
+
Cl2
Cl
R Br
R
+
Br2
Br2
Br
R
+ RCO3H
R
O
+ RCO3H
no
reaction
Benzene is a Weak Base and Poor Nucleophile
Stronger
base
H
+
Readily donates electrons
to an electrophile.
+
Donation of electrons would
interrupt ring resonance
(36 kcal / mole).
alkene
Weaker
base
H
benzene
A strong electrophile is
required - and often a
catalyst.
Benzene Reactivity
Benzene requires a strong electrophile and a catalyst
…..and then it undergoes substitution reactions, not addition.
Cl
+
Cl2
FeCl3
+ HCl
catalyst
substitution
compare:
+
Cl
Cl2
Cl
no catalyst
addition
Some Substitution Reactions of Benzene
Halogenation
Friedel-Crafts
Alkylation
AlCl3
+ Cl2
AlCl3
+ CH3Cl
Nitration
AlCl3
+ CH C
Cl
3
+
O
+ HO N
O
+ HO S OH
O
C CH
3
O
H2SO4
N O
+
-
O
O-
Sulfonation
CH3
O
O
Friedel-Crafts
Acylation
Cl
S OH
SO3
O
Blood
Alcohol
Level
Alcohols and Water
• alcohols are “monosubstituted” water, ROH,
hydrocarbon radical, R, substituted for one of
the hydrogen atoms in water, HOH
• alcohols form hydrogen bonds to other
alcohol molecules, increasing boiling point,
and to water, making them very soluble in
water
Classes of Alcohols
Oxidation of Alcohols
primary alcohol  aldehyde  carboxylic acids
RCH2OH  RCHO  RCOOH
secondary alcohols  ketones
RCHOHR’  RC=OR’
tertiary alcohols  No Reaction
Large Molecules Containing
Alcohol Groups
More Large
Molecules
Containing
Alcohol
Groups
O
OH
H3C
H3C
HO
HO
estrone
(female hormone,
an estrogen)
estradiol
(female hormone,
an estrogen)
OH
H3C
H3C
O
testostrone
(male hormone)
Ethanol is being tested in selected
areas as a fuel for automobiles
Source: AP/Wide World Photos
ALDEHYDES AND KETONES I
STRUCTURE
Aldehyde
O
C
R
H
R = H, alkyl, aryl
Ketone
O
C
R
R'
R and R' = alkyl or aryl
R and R' cannot be hydrogen!
Cinnamaldehyde produces the
characteristic odor of cinnamon
Source: Visuals Unlimited
NOMENCLATURE
IUPAC Nomenclature of Ketones
• Choose the longest continuous carbon chain that
contains the carbonyl carbon
• Number from the end of the chain closest to the
carbonyl carbon
• Ketone ending is -one
Do the ketones section of Organic Nomenclature
program!
EXAMPLES
O
C
CH 3
CH 2
CH 2
CH 3
2-Pentanone
O
CH3
C
CH2
CH2
CH
CH3
CH2
CH3
4-Ethyl-3-hexanone
O
CH
CH3
CH3
3-Isopropylcyclopentanone
or 3-(1-Methylethyl)cyclopentanone
KETONES
Common, or Trivial, Names
• Name each group attached to the carbonyl group
as an alkyl group
• Combine into a name, according to the pattern:
alkyl alkyl’ ketone
NOTE: This is not all one word!
Example of Common Names
O
C
CH 3
CH 2
CH 2
CH 3
Methyl propyl ketone
O
CH3
C
CH2
CH3
CH2
Diethyl ketone
SPECIAL CASES
O
O
C
C
CH3
CH3
dimethyl ketone
diphenyl ketone
acetone
benzophenone
A common laboratory
solvent and cleaning
agent
KNOW
THESE
O
C CH3
methyl phenyl ketone
acetophenone
IUPAC Nomenclature of Aldehydes
• Choose the longest continuous carbon chain that
contains the carbonyl carbon
• Number from the end of the chain closest to the
carbonyl carbon (carbon #1!)
• Aldehyde ending is -al
Do the aldehydes section of Organic Nomenclature
program.
EXAMPLES
H3C
CH2
CH2
CH2
C
aldehyde group is
always carbon 1
O
H
pentanal
Cl
4
CH3
3
CH
1
2
C
CH
CH3
O
H
2-chloro-3-methylbutanal
Common Names of the Aldehydes
H
O
O
O
C
C
C
CH3
H
Formaldehyde
1
H3C CH2 C
H
H3C CH2
Acetaldehyde
2
H
Propionaldehyde
3
O
O
C
C
H
H3C CH2 CH2 C
Butyraldehyde
Valeraldehyde
4
5
H
O
C
H3C CH2 CH2 CH2 CH2
Caproaldehyde
6
H
RECOGNIZE
THESE
O
SPECIAL CASES
C
H
H
O
C H
formaldehyde
O
benzaldehyde
C
H
CH3
acetaldehyde
KNOW
THESE
Figure 22.13: Some common
ketones and akdehydes
Figure 22.14: Some carboxylic
acids
Computer-generated space-filling
model of acetylsalicylic acid
(aspirin)
Source: Photo Researchers, Inc.