© a2 019 15-jul-12. structure of benzene benzene = c 6 h 6 its structure was a mystery for many...
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© www.chemsheets.co.uk A2 019 15-Jul-12
STRUCTURE OF BENZENE
Benzene = C6H6
Its structure was a mystery for many years - until Kekule’s dream.
STRUCTURE OF BENZENE
Problems with Kekule’s structure:
1) C-C bonds are all the same length (between C-C and C=C length).
2) Benzene does not undergo addition reactions readily (e.g. with bromine water).
3) H hydrogenation about 152 kJ mol-1 less than expected.
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C C
C
CC
C HH
H H
H H
STRUCTURE OF BENZENE
HYDROGENATION OF BENZENE
-120
-240
-360
-208
152
Energy(kJ/mol)
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NAMING AROMATIC COMPOUNDS
methylbenzene(toluene)
CH3 Cl NO2 COOH
chlorobenzene nitrobenzene benzenecarboxylic acid(benzoic acid)
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NAMING AROMATIC COMPOUNDS
1,3-dimethylbenzene(m-xylene)
4-methyl-1-chlorobenzene
2-hydroxybenzenecarboxylic acid
CH3
CH3
CH3
Cl
COOH
OH
COOH
NO2O2N
3,5-dinitrobenzenecarboxylic acid
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NAMING AROMATIC COMPOUNDS
phenylamine(aniline)
2-phenylbutane
phenylethene phenylethanone
NH2
CH CH2
CH2CH3 CH2 CH3
CO CH3
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NAMING AROMATIC COMPOUNDS
phenylethanoate methyl benzenecarboxylate(methyl benzoate)
N-phenylethanamide
OC
CH3
O
CO O
CH3
NH C
O
CH3
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NAMING AROMATIC COMPOUNDS
phenol benzene-1,2-diol
2,4,6-trichlorophenol(TCP)
OH
OH
Cl
Cl
Cl
OH
OH
OH
NO2
2-nitrophenol
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NITRATION
+ HNO3 + H2O
NO2
nitrobenzene
Conditions conc HNO3
conc H2SO4 catalyst
50ºC
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-H+
Formation of electrophile
HNO3
+ 2 H2SO4 + 2 HSO4-
+ H3O+
NO2
+
Reaction of electrophile with aromatic compound
NO2
NO2+ NO2
+H
nitronium ion
NITRATION – ELECTROPHILIC SUBSTITUTION
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NITRATION
Equation (name product)
Conditions
Mechanism
CH3CH3
NO2
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NITRATION
2-methylnitrobenzene
Conditions conc HNO3
conc H2SO4 catalyst
50ºC
CH3
+ HNO3 + H2O
CH3
NO2
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NITRATION
Uses of nitro compounds:
1) as explosives
2) to make aromatic amines (used to make dyes)
CH3
NO2
NO2
O2N
1,3,5-trinitrotolueneTNT
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FRIEDEL-CRAFTS ACYLATION
aromatic ketone
Conditions AlCl3 catalyst
R C
O
Cl+
CR O
+ HCl
+
CR O
+ R C
O
O C
O
R R C
O
OH
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FRIEDEL-CRAFTS ACYLATION
WARNING! - do not mix
Friedel-Crafts acylation & other acylations
(needs AlCl3)
Swap H on benzene ring
for acyl group
H H N
H
R
H O R
Swap H on O/N
for acyl group© www.chemsheets.co.uk A2 019 15-Jul-12
FRIEDEL-CRAFTS ACYLATION
WARNING! - Classic question to test this
NH2 NHCOCH3
CH3COCl
H replaced is on N not benzene ring.
This is NOT Friedel-Crafts acylation!
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Formation of electrophile
AlCl3
+ RCOCl +
AlCl4–+
C
O
R
acylium ion
OR
AlCl3
+ R-C-O-C-R +
–
+
C
O
R
acylium ion
O
O R-C-O-AlCl3
O
FRIEDEL-CRAFTS ACYLATION – ELECTROPHILIC SUBSTITUTION
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-H+
Reaction of electrophile with aromatic compound
CC
+H+
C
O
R
O
RO
R
FRIEDEL-CRAFTS ACYLATION – ELECTROPHILIC SUBSTITUTION
AlCl4– + H+ AlCl3 + HCl
+ H+ + AlCl3– R-C-O-AlCl3
O
R-C-OH
O
or
Regeneration of catalyst
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Equation
Conditions
Mechanism
FRIEDEL-CRAFTS ACYLATION
CH3CH3
CO CH2CH3
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Conditions AlCl3 catalyst
FRIEDEL-CRAFTS ACYLATION
CH3
CO CH2CH3
CH3
+ CH3CH2 C
O
Cl+ HCl
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