solomons and fryhle

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solomons and fryhle
Organic chemistry I
Zdeněk Friedl
Chapter 9
Aromatic hydrocarbons
Solomons & Fryhle: Organic
Chemistry 8th Ed., Wiley 2004
Aromatic hydrocarbons
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structure of aromates, delocalization energy
Hückel’s rule
type of aromatic hydrocarbons
reaction scheme of aromates
electrophilic aromatic substitution SEAr
Friedel-Crafts alkylation and acylation
further important SEAr reactions
substituent regioselectivity in SEAr reactions
side-chain reactions
oxidation and reduction of aromates
2
The orbital structure of benzene
An electrostatic potential map of benzene
(a) 6 sp2 orbitals connected into a ring by σ-bonds
(b) 6 pz orbitals of benzene ring
(c) overlap of pz orbitals a delocalized structure of benzene
3
The delocalization energy of benzene
A difference between heats of hydrogenation
of cyclohexatriene (theor) and benzene
4
The Hückel’s rule of aromaticity
(4n+2) π electrons
(n=0,1,2,3...)
5
Polycyclic aromatic hydrocarbons
PAHs
An enzymatic oxidation to reactive epoxides a alkylation of DNA
6
Nonbenzenoid aromatic compounds
AZULENE
delocalization energy of 205 kJ mol-1
The electrostatic potential map of azulene: there is substantial separation of
charge between the rings a an appreciable dipole moment
7
Nonbenzenoid aromatic compounds
FULLERENES
(C60 buckminsterfullerene)
8
Heterocyclic aromatic compounds
p-orbital structure of
PYRIDINE
PYRROLE
9
Summary of benzene reactivity
10
The reaction scheme of aromatic compounds
SR
oxidation
R CH
α 2
S EAr
CH
CH2CH3
α 2
AE
AR
CH CH R
11
SEAr
Summary of basic substitution reactions
12
SEAr
A general mechanism for the reaction
13
SEAr
The reaction coordinate of substitution reaction
14
SEAr
The electrophilic aromatic bromination
15
SEAr
Bromination of condensed aromates
α
β
α - kinetic controlled
β - thermodynamic controlled
Br
Br H
Br 2
- HBr
g
g
Br H
16
SEAr
The electrophilic aromatic nitration
17
SEAr
An alternative course of electrophilic aromatic
nitration
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SEAr
The electrophilic aromatic sulfonation
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SEAr
Friedel-Crafts alkylation I
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SEAr
Friedel-Crafts alkylation II
21
SEAr
Friedel-Crafts alkylation III
An industrial synthesis of STYRENE
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SEAr
Friedel-Crafts acylation I
23
SEAr
Friedel-Crafts acylation II
A generation of the REAGENT (acylium cation)
24
SEAr
Friedel-Crafts acylation III
A mechanism for the substitution reaction
25
SEAr
Selected electrophilic substitution reactions
CHLOROMETHYLATION
CH2=O + HCl + ZnCl2 g CH+2-OH [ZnCl3]- a a Ar-CH2-Cl
GATTERMANN-KOCH
C≡O + HCl + AlCl3 g CH+=O [AlCl4]- a Ar-CH=O
GATTERMAN
HCN + HCl + AlCl3 g CH+=NH [AlCl4]- a a Ar-CH=O
HOUBEN-HOESCH
R-CN + HCl + AlCl3 g RC+=NH [AlCl4]- a a Ar-(C=O)-R
REIMER-TIEMANN
CHCl3 + NaOH g CCl2 a a Ar-CH=O
(activated aromates)
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SEAr
Restrictions of Friedel-Crafts reactions
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SEAr
The synthesis of α-tetralone
F-C acylation a Clemmensen reduction a F-C acylation
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SEAr
Substitution effects
vs.
regioselectivity I
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SEAr
Substitution effects vs. regioselectivity II
A classification of substituents
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SEAr
Activating substituents a ortho-para orientation
(+ I, + M) ; (- I, + M) effect
31
SEAr
Halogenes a ortho-para orientation
(- I + M) effect: a deactivation of aromatic ring
32
SEAr
The reaction coordinates
of benzene vs. chlorobenzene
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SEAr
Deactivating substituents a meta orientation
(- I) ; (- M) ; (- I – M) effect
34
SEAr
Stability of σ-complex vs. nature of substituent
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SEAr
Summary of electrophilic aromatic
substitution reactions
36
Oxidation of alkylbenzene side-chain
37
AE/AR
Addition on C=C bond of alkenylbenzenes
A regioselectivity of AE a AR reactions
38
SR
Halogenation of alkylbenzene side-chain
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The regioselectivity of benzyl halogenation
40
An oxidation of aromatic hydrocarbons
O
COOH
O2
V2O5
g
COOH
O
O
COOH
O2
V2O5
g
COOH
O
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An industrial problem to be solved
OH
Ox
cat
INNOCENTIVE 2242048
Direct oxidation of benzene to phenol
Deadline: November 29, 2004
Reward: $ 45,000
Further problems can be found at www.innocentive.com
42
AR
Reduction of aromatic hydrocarbons
43
Summary of aromate synthetic reactions
44

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