arenes and aromaticity - p.g.g.c.g.-11, e-content...
TRANSCRIPT
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ARENES AND AROMATICITY
By Dr.Harpreet Kaur
Asst.Prof. PGGCG-11
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Arenes and Aromaticity
• Benzene has four degrees of unsaturation, making it a highly unsaturated hydrocarbon.
• Whereas unsaturated hydrocarbons such as alkenes, alkynes and dienes readily undergo addition reactions, benzene does not.
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• Benzene does react with bromine, but only in the presence of FeBr3 (a Lewis acid), and the reaction is a substitution, not an addition.
• Proposed structures of benzene must account for its high degree of unsaturation and its lack of reactivity towards electrophilic addition.
• August Kekulé proposed that benzene was a rapidly equilibrating mixture of two compounds, each containing a six-membered ring with three alternating π bonds.
• In the Kekulé description, the bond between any two carbon atoms is sometimes a single bond and sometimes a double bond.
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• These structures are known as Kekulé structures.
• Although benzene is still drawn as a six-membered ring with alternating π bonds, in reality there is no equilibrium between the two different kinds of benzene molecules.
• Current descriptions of benzene are based on resonance and electron delocalization due to orbital overlap.
• In the nineteenth century, many other compounds having properties similar to those of benzene were isolated from natural sources. Since these compounds possessed strong and characteristic odors, they were called aromatic compounds. It should be noted, however, that it is their chemical properties, and not their odor, that make them special.
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Any structure for benzene must account for the following facts:1. It contains a six-membered ring and three additional
degrees of unsaturation.2. It is planar.3. All C—C bond lengths are equal.
The Kekulé structures satisfy the first two criteria but not the third, because having three alternating π bonds means that benzene should have three short double bonds alternating with three longer single bonds.
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• The resonance description of benzene consists of two equivalent Lewis structures, each with three double bonds that alternate with three single bonds.
• The true structure of benzene is a resonance hybrid of the two Lewis structures, with the dashed lines of the hybrid indicating the position of the π bonds.
• We will use one of the two Lewis structures and not the hybrid in drawing benzene. This will make it easier to keep track of the electron pairs in the π bonds (the π electrons).
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• Because each π bond has two electrons, benzene has six π electrons.
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• In benzene, the actual bond length (1.39 Å) is intermediate between the carbon—carbon single bond (1.53 Å) and the carbon—carbon double bond (1.34 Å).
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• A benzene substituent is called a phenyl group, and it can be abbreviated in a structure as “Ph-”.
• Therefore, benzene can be represented as PhH, and phenol would be PhOH.
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• The benzyl group, another common substituent that contains a benzene ring, differs from a phenyl group.
• Substituents derived from other substituted aromatic rings are collectively known as aryl groups.
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[3] A molecule must be completely conjugated.
Aromatic compounds must have a p orbital on every atom.
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[4] A molecule must satisfy Hückel’s rule, and containa particular number of π electrons.
Benzene is aromatic and especially stable because it contains 6 π electrons. Cyclobutadiene is antiaromatic and especially unstable because it contains 4 π electrons.
Hückel's rule:
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Note that Hückel’s rule refers to the number of π electrons, not the number of atoms in a particular ring.
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1. Aromatic—A cyclic, planar, completely conjugated compound with 4n + 2 π electrons.
2. Antiaromatic—A cyclic, planar, completely conjugated compound with 4n π electrons.
3. Not aromatic (nonaromatic)—A compound that lacks one (or more) of the following requirements for aromaticity: being cyclic, planar, and completely conjugated.
Considering aromaticity, a compound can be classified in one of three ways:
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Note the relationship between each compound type and a similar open-chained molecule having the same number of π electrons.
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Examples of Aromatic Rings
• Completely conjugated rings larger than benzene are also aromatic if they are planar and have 4n + 2 π electrons.
• Hydrocarbons containing a single ring with alternating double and single bonds are called annulenes.
• To name an annulene, indicate the number of atoms in the ring in brackets and add the word annulene.
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• [10]-Annulene has 10 π electrons, which satisfies Hückel's rule, but a planar molecule would place the two H atoms inside the ring too close to each other. Thus, the ring puckers to relieve this strain.
• Since [10]-annulene is not planar, the 10 π electrons can’t delocalize over the entire ring and it is not aromatic.
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Electrophilic Aromatic Substitution
Ar-H = aromatic compound1. Nitration
Ar-H + HNO3, H2SO4 Ar-NO2 + H2O
2. Sulfonation
Ar-H + H2SO4, SO3 Ar-SO3H + H2O
3. Halogenation
Ar-H + X2, Fe Ar-X + HX
4. Friedel-Crafts alkylation
Ar-H + R-X, AlCl3 Ar-R + HX
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Friedel-Crafts alkylation (variations)
a) Ar-H + R-X, AlCl3 Ar-R + HX
b) Ar-H + R-OH, H+ Ar-R + H2O
c) Ar-H + Alkene, H+ Ar-R
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NO2
SO3H
Br
CH2CH3
HNO3
H2SO4
SO3
H2SO4
Br2, Fe
CH3CH2-Br
AlCl3
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toluene
CH3
CH3
CH3CH3
CH3
CH3 CH3
CH3
CH3
Br
Br
NO2
NO2
SO3H
SO3H
HNO3
H2SO4
SO3
H2SO4
Br2, Fe
+
+
+
faster than the same reactions with benzene
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nitrobenzene
NO2
NO2
NO2
NO2
NO2
NO2
NO2
SO3H
Cl
HNO3
H2SO4
H2SO4
SO3
Cl2, Fe
slower than the same reactions with benzene
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Substituent groups on a benzene ring affect electrophilic aromatic substitution reactions in two ways:
1) reactivity
activate (faster than benzene)
or deactivate (slower than benzene)
2) orientation
ortho- + para- direction
or meta- direction
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-CH3
activates the benzene ring towards EAS
directs substitution to the ortho- & para- positions
-NO2
deactivates the benzene ring towards EAS
directs substitution to the meta- position
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Common substituent groups and their effect on EAS:
-NH2, -NHR, -NR2-OH-OR-NHCOCH3-C6H5-R-H-X-CHO, -COR-SO3H-COOH, -COOR-CN-NR3+
-NO2
incr
easi
ng re
activ
ity
ortho/para directors
meta directors
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OCH3
CHO
Br
Br2, Fe
HNO3, H2SO4
H2SO4, SO3
OCH3Br
OCH3
Br
+ faster than benzene
CHO
NO2
slower than benzene
+
Br BrSO3H
SO3H
slower than benzene
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If there is more than one group on the benzene ring:
1. The group that is more activating (higher on “the list”) will direct the next substitution.
2. You will get little or no substitution between groups that are meta- to each other.
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CH3
OH
NHCOCH3
CH3
CHO
OCH3
Br2, Fe
HNO3, H2SO4
Cl2, Fe
CH3
OHBr
NHCOCH3
CH3
NO2
CHO
OCH3Cl
CHO
OCH3
Cl+
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Orientation and synthesis. Order is important!
synthesis of m-bromonitrobenzene from benzene:
NO2
Br
NO2HNO3
H2SO4
Br2, Fe
synthesis of p-bromonitrobenzene from benzene:
Br Br Br
NO2
NO2+
Br2, Fe HNO3
H2SO4
You may assume that you can separate a pure para- isomer from an ortho-/para- mixture.
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note: the assumption that you can separate a pure para isomer from an ortho/para mixture does not apply to any other mixtures.
Br Br
Br
BrBr
NO2 NO2
Br
NO2
BrBr
NO2
Br
Br
Br
Br
NO2+
+
Br2, Fe Br2, Fe
Br2, Fe Br2, FeHNO3H2SO4
HNO3H2SO4
synthesis of 1,4-dibromo-2-nitrobenzene from benzene
separate pure para isomer from ortho/para mixture
cannot assume that these can be separated!
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CH3
CH3
CH3
COOH
COOH COOH
CH3 COOH
NO2
NO2 NO2
+ ortho-
CH3Br
AlCl3
CH3Br
CH3Br
AlCl3
AlCl3
KMnO4
KMnO4
KMnO4
heat
heat
heat
HNO3
H2SO4
HNO3
H2SO4
synthesis of benzoic acids by oxidation of –CH3
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+HO-NO2 + H2SO4 H2O-NO2 + HSO4-
+ +H2O-NO2 H2O + NO2
H2SO4 + H2O HSO4- + H3O+
HNO3 + 2 H2SO4 H3O+ + 2 HSO4- + NO2+
nitration
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nitration:
1) HONO2 + 2 H2SO4 H3O+ + 2 HSO4- + NO2+
2) + NO2+ RDS
electrophile
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H
NO2
H
NO2
H
NO2
H
NO2
resonance
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Mechanism for nitration:
1) HONO2 + 2 H2SO4 H3O+ + 2 HSO4
- + NO2+
2) + NO2+
H
NO23)
RDS
NO2 + H+
H
NO2
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Mechanism for sulfonation:
1) 2 H2SO4 H3O+ + HSO4- + SO3
2) + SO3
RDS
H
SO3-
3)H
SO3-SO3
- + H+
4) SO3- SO3H+ H3O
+ + H2O
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Mechanism for halogenation:
1) Cl2 + AlCl3 Cl-Cl-AlCl3
2) + Cl-Cl-AlCl3RDS
H
Cl+ AlCl4
-
3)H
Cl+ AlCl4- Cl + HCl + AlCl3
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Mechanism for Friedel-Crafts alkylation:
1) R-X + FeX3 R + FeX4-
2) + RRDS
3)
H
R
H
R + FeX4- R + HX + FeX3
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1) R-OH + H+ ROH2+
3) + RRDS
4)
H
R
H
RR
2) ROH2+ R + H2O
+ H+
Mechanism for Friedel-Crafts with an alcohol & acid
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2) + RRDS
3)
H
R
H
RR
1) C C + H+ R
+ H+
Mechanism for Friedel-Crafts with alkene & acid:
electrophile in Friedel-Crafts alkylation = carbocation
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Electrophilic Aromatic Substitution mechanism:
1) + Y+Z-RDS
H
Y+ Z-
2)H
Y+ Z- Y + HZ
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Substituent groups on a benzene ring affect the reactivity and orientation in the way they do?
electronic effects, “pushing” or “pulling” electrons by the substituent.
Electrons can be donated (“pushed”) or withdrawn (“pulled”) by atoms or groups of atoms via:
Induction – due to differences in electronegativities
Resonance – delocalization via resonance
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NH
H
unshared pair of electrons on the nitrogenresonance donating groups(weaker inductive withdrawal)
NR
R
NR
H
NRR
R strong inductive withdrawal(no unshared pair of electrons on thenitrogen & no resonance possible
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H3C CO
NH
resonance donation(weaker inductive withdrawal)
HO
resonance donation(weaker inductive withdrawal)
RO
resonance donation(weaker inductive withdrawal)
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resonance donation
H3Cinductive donationsp3 sp2 ring carbon
inductive withdrawal X—
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HC
O
HOC
O
ROC
O
RC
O
resoance withdrawal andinductive withdrawal
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NO
O
resonance andinductive withdrawal
resonance andinductive withdrawal
CN
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Common substituent groups and their effect on reactivity in EAS:
-NH2, -NHR, -NR2-OH-OR-NHCOCH3 electron donating-C6H5-R-H-X-CHO, -COR-SO3H-COOH, -COOR electron withdrawing-CN-NR3+
-NO2
incr
easi
ng re
activ
ity
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Electron donating groups activate the benzene ring to electrophilic aromatic substitution.
1. electron donating groups increase the electron density in the ring and make it more reactive with electrophiles.
2. electron donation stabilizes the intermediate carbocation, lowers the Eact and increases the rate.
H Y
CH3
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H Y
NO2
Electron withdrawing groups deactivate the benzene ring to electrophilic aromatic substitution.
1. electron withdrawing groups decrease the electron density in the ring and make it less reactive with electrophiles.
2. electron withdrawal destabilizes the intermediate carbocation, raising the Eact and slowing the rate.
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CF3
PH2
PO3H
electron withdrawing = deactivating & meta-director
electron withdrawing = deactivating & meta-director
electron donating = activating & ortho-/para-director
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Br2, FeBr + ortho-
NO2Br2, Fe
NO2Br + ortho-
O
OBr2, Fe
O
O
Br+ ortho-
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G G G
G G G
G G
H H HY Y Y
HY
HY
HY
H Y H Y
G
H Y
ortho-attack
meta-attack
para-attack
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G
HY
G
H Y
If G is an electron donating group, these structures are especially stable.
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G G G
G G G
G G
H H HY Y Y
HY
HY
HY
H Y H Y
G
H Y
ortho-attack
meta-attack
para-attack
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Electron donating groups stabilize the intermediate carbocations for ortho- and para- in EAS more than for meta-. The Eact’s for ortho-/para- are lower and the rates are faster.
Electron donating groups direct ortho-/para- in EAS
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G
HY
G
H Y
If G is an electron withdrawing group, these structures are especially unstable.
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G G G
G G G
G G
H H HY Y Y
HY
HY
HY
H Y H Y
G
H Y
ortho-attack
meta-attack
para-attack
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Electron withdrawing groups destabilize the intermediate carbocations for ortho- and para- in EAS more than for meta-. The Eact’s for ortho-/para- are higher and the rates are slower.
Electron withdrawing groups direct meta- in EAS
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Halogens are electron withdrawing but are ortho/para directing in EAS.
The halogen atom is unusual in that it is highly electronegative but also has unshared pairs of electrons that can be resonance donated to the carbocation.
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X X X
X X X
X X
H H HY Y Y
HY
HY
HY
H Y H Y
X
H Y
X
H Y
X
HY
ortho-
meta-
para-
halogens are deactivating in EAS but direct ortho and para
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Common substituent groups and their effect on EAS:
-NH2, -NHR, -NR2-OH-OR-NHCOCH3-C6H5-R-H-X-CHO, -COR-SO3H-COOH, -COOR-CN-NR3+
-NO2
incr
easi
ng re
activ
ity
ortho/para directors
meta directors
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Arenes: compounds containing both aliphatic and aromatic parts.
Alkylbenzenes
Alkenylbenzenes
Alkynylbenzenes
Etc.
Emphasis on the effect that one part has on the chemistry of the other half.
Reactivity & orientationcc
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Example: ethylbenzene
EAS in the aromatic part
-CH2CH3 activates and directs ortho- & para-
CH2
CH3CH2
CH3CH2
CH3
CH2 CH3 CH CH3
Br2, Fe Br
Br
Br2, heat
Br+ HBr
+
Free radical halogenation in the side chain
-C6H5 activates and directs benzyl
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Alkylbenzenes, nomenclature:
Special names
CH3 CH3CH3
CH3
CH3
CH3
CH3
toluene o-xylene m-xylene p-xylene
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others named as “alkylbenzenes”:
CHH3C CH3 CH2
H2CCH3
H2C
CHCH3
CH3
isopropylbenzene n-propylbenzene isobutylbenzene
CH2
CH2
CH3
CH3
o-diethylbenzene n-butylbenzene
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Use of phenyl C6H5- = “phenyl”
CH2CH2
2-methyl-3-phenylheptane 1,2-diphenylethane
do not confuse phenyl (C6H5-) with benzyl (C6H5CH2-)
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Alkenylbenzenes, nomenclature:
CH=CH2
styrene
CH2CH=CH2
3-phenylpropene(allylbenzene)
(Z)-1-phenyl-1-butene
Special name
Rest are named as substituted alkenes
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Alkynylbenzenes, nomenclature:
C CH
phenylacetylene5-phenyl-2-hexyne
phenylethyne
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Alcohols, etc., nomenclature:
CHH3C OH
1-phenylethanol
α−phenylethyl alcohol
CH2OH
benzyl alcohol
1-chloro-2-phenylethane
β -phenylethyl chloride
CH2CH2-Cl
cyclohexylbenzene
phenylcyclohexane
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Alkylbenzenes, syntheses:
1. Friedel-Crafts alkylation
2. Modification of a side chain:
a) addition of hydrogen to an alkene
b) reduction of an alkylhalide
i) hydrolysis of Grignard reagent
ii) active metal and acid
c) Corey-House synthesis
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Modification of side chain:
Br
+ H2, Ni
+ Sn, HCl
Br
+ Mg; then H2o
ethylbenzene
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Friedel-Crafts:
Ar-H + R-X, AlCl3 Ar-R + HX
Ar-H + R-OH, H+ Ar-R + H2O
Ar-H + alkene, H+ Ar-R
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CH3CH3
CCH3
H3C CH3
+ H3C CCH3
BrCH3
AlCl3
+ CH3CH2-OH, H+ CH2CH3
+ CH2=CHCH3, H+ CHCH3
CH3isopropylbenzene
ethylbenzene
p-tert-butyltoluene
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H+cyclohexylbenzene
H3CCH2Cl
AlCl3CH2 CH3
ortho-p-benzyltoluene
CH2Cl2, AlCl32 CH2
diphenylmethane
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Friedel-Crafts limitations:
a) Polyalkylation
b) Possible rearrangement
c) R-X cannot be Ar-X
d) NR when the benzene ring is less reactive than bromobenzene
e) NR with -NH2, -NHR, -NR2 groups
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polyalkylation
CH3CH3Br, AlCl3
+CH3 CH3
CH3
CH3
+
CH3CH3
H3C
+
The alkyl group activates the ring making the products more reactive that the reactants leading to polyalkylation. Use of excess aromatic compound minimizes polyalkylation in the lab.
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The electrophile in Friedel Crafts alkylation is a carbocation:
R-X + AlX3 R+
R-OH + H+ R+
| |— C = C — + H+ R+
Carbocations can rearrange!
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rearrangement
+ CH3CH2CH2-Br, AlCl3
CHCH3H3C
AlCl3+
C CH3H3CCH3
+
H+
isopropylbenzene
tert-butylbenzene
2-methyl-2-phenylbutane
carbocation rearrangements are possible!
CH3CCH2CH3
CH3
CH3CHCH2-BrCH3
CH3CCH2-OHCH3
CH3
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n-alkylbenzenes cannot be made by Friedel-Crafts alkylation due to
carbocation rearrangements
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R-X cannot be Ar-X
+ R-X, AlCl3
R
+
XAlCl3
NR
The Ar-X bond is strong and does not break like the R-X bond!
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NR with rings less reactive than bromobenzene
Br
+ CH3CH2-Br, AlCl3
Br Br
CH2CH3
CH2CH3+
COOH
NO2
+ CH3-Br, AlCl3
+ CH3CH2-OH, H+
NR
NR
-CHO, -COR
-SO3H
-COOH, -COOR
-CN
-NR3+
-NO2
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NR with –NH2, -NHR, -NR2
NH2
+ CH3CH2-Cl, AlCl3 NR
NH2
+ AlCl3
NH2 AlCl3
Lewis base Lewis acid deactivated to EAS
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Friedel-Crafts limitations:
a) Polyalkylation
b) Possible rearrangement
c) R-X cannot be Ar-X
d) NR when the benzene ring is less reactive than bromobenzene
e) NR with -NH2, -NHR, -NR2 groups
In syntheses it is often best to do Friedel-Crafts alkylation in the first step!
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Alkylbenzenes, reactions:
1. Reduction
2. Oxidation
3. EAS
a) nitration
b) sulfonation
c) halogenation
d) Friedel-Crafts alkylation
4. Side chain
free radical halogenation
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Alkylbenezenes, reduction:
NR NR NR
NR
H2, Ni
H2, Ni
300oC, 100 atm.
CH3CH3
H2C
CH3
H2C
CH3
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Alkylbenezenes, oxidation:
NR NR NR
NR NR
KMnO4
KMnO4
heat
CH3CH3
H2C
CH3
COOH
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+ KMnO4, heat
+ KMnO4, heat
COOH
COOH
COOH
+ 2 CO2
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Oxidation of alkylbenzenes.
1) Syn
2) identification
C8H10:
H2C
CH3CH3
CH3
CH3
CH3
CH3
CH3 COOH
COOHCOOH
COOH
COOH
COOH
COOH
bp 136oC
bp 144oC
bp 139oC
bp 138oC
mp 122oC
mp 231oC
mp 348oC
mp 300oC
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Alkylbenzenes, EAS
CH2CH3CH2CH3
CH2CH3
CH2CH3 CH2CH3
CH2CH3 CH2CH3
CH2CH3CH2CH3
NO2
NO2
SO3H
SO3H
Br
Br
CH3
CH3
+
+
+
+HNO3, H2SO4
H2SO4, SO3
Br2, Fe
CH3Cl, AlCl3
-R is electron releasing. Activates to EAS and directs ortho/para
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Alkylbenzenes, free radical halogenation in side chain:
benzyl free radical
CH2CH3
CH2CH3
+ Cl2, heat
+ Br2, heat
CHCH3 CH2CH2-Cl
CHCH3
Cl
+
Br
91% 9%
only
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CH2CH3
benzyl free radical > 3o > 2o > 1o > CH3
CHCH3
CHCH3CHCH3 CHCH3.
.
.
.
X2 2 X.
+ X .
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Alkenylbenzenes, syntheses:
1. Modification of side chain:
a) dehydrohalogenation of alkyl halide
b) dehydration of alcohol
c) dehalogenation of vicinal dihalide
d) reduction of alkyne
(2. Friedel-Crafts alkylation)
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Alkenylbenzenes, synthesis modification of side chain
CHCH3
CHCH3
CHCH2
C
CH=CH2
CH
Br
OH
Cl Cl
styrene
KOH(alc)
H+, heat
Zn
H2, Pd-C
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Alkenylbenzenes, synthesis Friedel-Crafts alkylation
not normally used for alkenylbenzenes.
an exception:
+ CH2=CHCH2-Br, AlCl3 CH2CH=CH2
allylbenzene
+ CH2=CH-Br, AlCl3 NR
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Br
KOH(alc)conjugated with the ring
+ KOH, heat
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Alkenylbenzenes, reactions:
1. Reduction
2. Oxidation
3. EAS
4. Side chain
a) add’n of H2 j) oxymercuration
b) add’n of X2 k) hydroboration
c) add’n of HX l) addition of free rad.
d) add’n of H2SO4 m) add’n of carbenes
e) add’n of H2O n) epoxidation
f) add’n of X2 & H2O o) hydroxylation
g) dimerization p) allylic halogenation
h) alkylation q) ozonolysis
i) dimerization r) vigorous oxidation
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Alkenylbenzenes, reactions: reduction
CH=CH2
CH=CH2
+ H2, Ni
+ H2, Ni, 250oC, 1,500 psi
CH2CH3
H
CH2CH3
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Alkenylbenzenes, reactions oxidation
CH=CH2
CH=CH2
CH=CH2
CHCH2
COOH
CH=O
OHOH
+ CO2
+ O=CH2
KMnO4
heat
1. O3
2. Zn, H2O
KMnO4
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Alkenylbenzenes, reactions EAS?
CH=CH2
electrophilic aromatic substitution
electrophilic addition
alkenes are more reactive with electrophiles than aromatic rings!
CH=CH2 + Br2, Fe CHCH2Br Br
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In syntheses of alkenylbenzenes, the carbon-carbon double bond must be synthesized after any EAS reactions
CH2CH3 CH2CH3
CH=CH2
Cl
CHCH3
CH2=CH2
HF
Cl2, Fe+ ortho
CH2CH2-ClCl
Cl ClCl
Cl2, hv
KOH(alc)
p-chlorostyrene
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Alkenylbenzenes, reactions side chain:
CH=CHCH3 CH2CH2CH3
CHCHCH3
CHCH2CH3
CHCH2CH3
Br
Br
Br
OSO3H
H2, Ni
Br2, CCl4
HBr
H2SO4
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Benzyl carbocation
CH=CHCH3 + H+ CHCH2CH3
CHCH2CH3CHCH2CH3 CHCH2CH3
resonance stabilization of benzyl carbocation > 3o > 2o > 1o
-
104
CH=CHCH3 CHCH2CH3
CHCHCH3
CHCH2CH3
CH2CHCH3
OH
OH
Br
OH
OH
H2O, H+
Br2, H2O
1. H2O, Hg(OAc)2
2. NaBH4
1. (BH3)2
2. H2O2, NaOH
-
105
CH=CHCH3 CH2CHCH3
CH=CH2
CH=CHCH3
CH=CHCH3
CHCH2 n
polystyrene
Br
O
HBr, perox.
polymer.
CH2N2, hv
PBA
-
106
CH=CHCH3 + Br2, heat CH=CHCH2-Br
C CCH3
H
H
(E)-1-phenylpropene
CH3H OH
HO H
CH3HO H
H OH+
KMnO4
100 syn-oxidation; make a model!
-
107
Alkynylbenzenes, syntheses:
Dehydrohalogenation of vicinal dihalides
CH=CH2 CHCH2Br
Br
C CHBr2 1. KOH
2. NaNH2
HC CH3Br
KOH(alc)
H2C CH3
CH2=CH2
HF
-
108
Alkynylbenzenes, reactions:
1. Reduction
2. Oxidation
3. EAS
4. Side chain
a) reduction e) as acids
b) add’n of X2 f) with Ag+
c) add’n of HX g) oxidation
d) add’n of H2O, H+
-
109
Alkynylbenzenes, reactions: reduction
C C CH3 + 2 H2, Ni CH2CH2CH3
+ (xs) H2, Ni heat & pressure
C C CH3 + Li, NH3
+ H2, Pd-C
anti-
syn-
-
110
Alkynylbenzenes, reactions: oxidation
C C CH3
KMnO4, heat
O3; then Zn, H2O
COOH + HOOCCH3KMnO4
-
111
Alkynylbenzenes, reactions EAS?
C
electrophilic aromatic substitution
electrophilic addition
alkynes are more reactive with electrophiles than aromatic rings!
C + Br2, Fe C=CH
CH
CH
Br
Br
-
112
Alkynylbenzenes, reactions: side chain:
C C H C=CH
C
CCH3
Br
Br
Br
Br
Br
BrCBr
BrH
C=CH2Br
Br2
2 Br2
HBr
2 HBr
-
113
C CHH2O, H
+
CCH3
O
C CH
C CH
Na
Ag+
C
C
C-Na+
C-Ag+
C CCH3Ag+
NR, not terminal
-
114
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ARENES AND AROMATICITYSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 53Slide 54Slide 55Slide 56Slide 57Slide 58Slide 59Slide 60Slide 61Slide 62Slide 63Slide 64Slide 65Slide 66Slide 67Slide 68Slide 69Slide 70Slide 71Slide 72Slide 73Slide 74Slide 75Slide 76Slide 77Slide 78Slide 79Slide 80Slide 81Slide 82Slide 83Slide 84Slide 85Slide 86Slide 87Slide 88Slide 89Slide 90Slide 91Slide 92Slide 93Slide 94Slide 95Slide 96Slide 97Slide 98Slide 99Slide 100Slide 101Slide 102Slide 103Slide 104Slide 105Slide 106Slide 107Slide 108Slide 109Slide 110Slide 111Slide 112Slide 113THANK YOU