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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.

8

• 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).

9

• 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!

85

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

88

+ KMnO4, heat

+ KMnO4, heat

COOH

COOH

COOH

+ 2 CO2

89

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

90

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

91

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

92

CH2CH3

benzyl free radical > 3o > 2o > 1o > CH3

CHCH3

CHCH3CHCH3 CHCH3.

.

.

.

X2 2 X.

+ X .

93

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)

94

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

95

Alkenylbenzenes, synthesis Friedel-Crafts alkylation

not normally used for alkenylbenzenes.

an exception:

+ CH2=CHCH2-Br, AlCl3 CH2CH=CH2

allylbenzene

+ CH2=CH-Br, AlCl3 NR

96

Br

KOH(alc)conjugated with the ring

+ KOH, heat

97

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

98

Alkenylbenzenes, reactions: reduction

CH=CH2

CH=CH2

+ H2, Ni

+ H2, Ni, 250oC, 1,500 psi

CH2CH3

H

CH2CH3

99

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

100

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

101

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

102

Alkenylbenzenes, reactions side chain:

CH=CHCH3 CH2CH2CH3

CHCHCH3

CHCH2CH3

CHCH2CH3

Br

Br

Br

OSO3H

H2, Ni

Br2, CCl4

HBr

H2SO4

103

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