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Aromaticity
hydrocarbons
aliphatic aromatic
alkanes alkenes alkynes
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Aliphatic compounds: open-chain compounds andring compounds that are chemically similar to open-chain compounds. Alkanes, alkenes, alkynes, dienes,alicyclics, etc.
Aromatic compounds: unsaturated ring compoundsthat are far more stable than they should be and resistthe addition reactions typical of unsaturated aliphaticcompounds. Benzene and related compounds.
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The structure of benzene
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All the chemistry they knew suggested that anysubstance with a double or triple bond would bevery reactive and react readily with HBr in the
dark.
Benzene did not, it was surprisinglyunreactive
This new hydrocarbon isolated by Michael Faradayin 1825
The molecular formula is C6H6 suggesting thatthe molecule contained a large number of doublebonds.
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Benzene. This aromatic hydrocarbon was firstdiscovered in 1825 but its structure was not
generally agreed upon until 1946
In 1865 after a dream about a snake biting itsown tale, Kekul suggested the following
structure for benzene
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Facts about benzene:
a) Formula = C6H6b) Isomer number:
one monosubstituted isomer C6H5Y
three disubstituted isomers C6H4Y2
c) Benzene resists addition reaction,undergoes substitution reactions.
d) From X-ray, all of the CC bonds inbenzene are the same length andintermediate in length between single and
double bonds.
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Benzene is a flatmolecule, with all atomsin the same plane, (bond
angle 120)
When the benzene ring isattached to an aliphatic
skeleton, it is called thephenyl group. The formulaof a phenyl group id C6H5.
Any compoundwhere the ratio ofC:H is about 1:1 islikely to contain a
benzene ring.
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ISOMER
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Reactions of benzene:
1. Nitration
C6H6 + HNO3 C6H5NO2 + H2O
2. Sulfonation
C6H6 + H2SO4 C6H5SO3H + H2O
3. Halogenation
C6H6 + X2 C6H5X + HX
4. Freidel-Crafts alkylation
C6H6 + RX C6H5R + HX
substitutions
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Hckels Rule
If the compound has a continuous ring of
overlappingp orbitals and has 4N+ 2
electrons, it is aromatic.
If the compound has a continuous ring of
overlappingp orbitals and has 4Nelectrons,
it is antiaromatic.
=>
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4n + 2 = 4
n = 0.5
not aromaticantiaromatic
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4n + 2 = 8
n = 1.5
nonplanar
nonaromatic
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4n + 2 = 10
n = 2
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Naming benzene molecules
1.2-dimethyl
benzene
1,3-dimethyl
benzene
1,4-dimethyl
benzene
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naftalen antracen fenantren tetracen
trifenilen piren krisen
Fused ring systems
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H
H H
H
H
HH
H
Naftalen
H
H H
HH
H
H
H
H
H
Antracen
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Fenantren
H
H H
H
H
H
H
HH
H
H
H
H
H
H
H
H
H
H
H
H H
Koronen
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Naftalen: nomenklature
monosubstitusi: - 1-- 2-
NO2
2-nitronaphthalene-nitronaphthalene
OH NH2 SO3H
-naphthol -naphthylamine -naphthalenesulfonic acid
also
2-nitronaftalen-nitronaftalen
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1-nitronaftalen
-nitronaftalen
1-bromnaftalen
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Common Names of
Benzene DerivativesOH OCH3NH2
CH3
phenol toluene aniline anisole
C
H
CH2 C
O
CH3C
O
H
C
O
OH
styrene acetophenone benzaldehyde benzoic acid
=>
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Mercedes Benzene
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Disubstituted Benzenes
The prefixes ortho-, meta-, and para- arecommonly used for the 1,2-, 1,3-, and 1,4-
positions, respectively.Br
Bro-dibromobenzene o
1,2-dibromobenzene
HO
NO2
p-nitrophenol or4-nitrophenol
=>
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Br
Br
NO2
Cl
CH3
Br
o-dibromobenzene m-chloronitrobenzene p-bromotoluene
1,2-dibromobenzene 3-chloro-1-nitrobenzene 4-bromotoluene
Br
Br
If more than two groups on the ring, use numbers!
BrNH
2Br
Br
Br
1,2,4-tribromobenzene 2,4,6-tribromoaniline
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3 or More Substituents
Use the smallest possible numbers, butthe carbon with a functional group is #1.
NO2
NO2
O2N
1,3,5-trinitrobenzen
NO2
NO2
O2N
OH
2,4,6-trinitrophenol
=>
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Common Names for
Disubstituted Benzenes
CH3
CH3
CH3
CH3H3C
CH3
CO OH
OH
H3Cm-xylene mesitylene o-toluic acid p-cresol
=>
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Chloro Methyl benzene
2,4,6-trichlorophenol
benzene-1,4-dicarboxylic aci
2-hydroxybenzoic acid
phenolphenylethanone
phenyl ethanoate
phenylamine
chlorobenzene
phenylethene
nitrobenzene
Benzoic acid
Methyl 3-nitrobenzoate
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Phenyl and Benzyl
Br
phenyl bromide
CH2Br
benzyl bromide
Phenyl indicates the benzene ringattachment. The benzyl group hasan additional carbon.
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See you..