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Benzene and Aromaticity

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Benzene and Aromaticity. Bonding in Benzene. Proposed Benzene Structures. C 6 H 6 reacts with Br 2 to form one isomer of C 6 H 5 Br. Other Conjugated Hydrocarbon Rings Annulenes. D H hyd Data Illustrates Stability. Benzene Representations. Molecular Orbitals of Benzene. - PowerPoint PPT Presentation
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Benzene and Aromaticity
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Page 1: Benzene and Aromaticity

Benzene and Aromaticity

Page 2: Benzene and Aromaticity

Bonding in Benzene

Page 3: Benzene and Aromaticity

Proposed Benzene Structures

Dewar benzene Ladenburg benzene

Kekule benzene

Page 4: Benzene and Aromaticity

C6H6 reacts with Br2 to form one isomer of C6H5Br

Ladenburg benzene

Kekule benzene

Br2, cat.1 unique C6H5Br Br2, cat.

3 unique C6H4Br2(+ HBr) (+ HBr)

C6H6

C6H6

Br2, cat.

Br

Br2, cat.1,2- 1,3- & 1,4-dibromo

+ HBr

Page 5: Benzene and Aromaticity

Other Conjugated Hydrocarbon RingsAnnulenes

Page 6: Benzene and Aromaticity

Hhyd Data Illustrates Stability

Page 7: Benzene and Aromaticity

Benzene Representations

Page 8: Benzene and Aromaticity

Molecular Orbitals of Benzene

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+++ +

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+

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+

+

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+

--

- -

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+

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Page 9: Benzene and Aromaticity
Page 10: Benzene and Aromaticity

M.O.’s of Cyclobutadiene

+

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+

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+

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1 3

1

4

Page 11: Benzene and Aromaticity

6 Electrons is Stable4 or 8 Electrons is not

Page 12: Benzene and Aromaticity

Huckel’s Rule: 4N + 2

Page 13: Benzene and Aromaticity

In Order to Exhibit Aromaticity a Compound Must…

-         Cyclic-         Planar-         Conjugated throughout-         Has a “Huckel #” of electrons

o       4N + 2 where N is any integer or 0         hence, 2,6,10,14 e-

naphthalene

Page 14: Benzene and Aromaticity

Naphthalene

Page 15: Benzene and Aromaticity

Pyridine, an Aromatic Heterocycle

Page 16: Benzene and Aromaticity

Pyridine as a Base

Page 17: Benzene and Aromaticity

Pyrrole

Page 18: Benzene and Aromaticity

Pyrrole as a Base

Page 19: Benzene and Aromaticity

Other Aromatic Heterocycles

Page 20: Benzene and Aromaticity

Cyclopentadiene as an AcidpKa = 16

Page 21: Benzene and Aromaticity

Cyclopentadienyl ion:One is Aromatic, one is Antiaromatic

Page 22: Benzene and Aromaticity

Resonance Depictions of the Ions

Page 23: Benzene and Aromaticity

Tropylium Ion

Page 24: Benzene and Aromaticity

Aromatic?

c)b)a)NH

BHO

Page 25: Benzene and Aromaticity

Aromatic, Anti-Aromatic or Nonaromatic?

c)

N

N

H

H

b) a)

Page 26: Benzene and Aromaticity

Some Well-known Aromatic Compounds

CO2HOCCH3

O

acetyl salicylic acid

HO2Cibuprofin

N

NH

CH3HO2C

lysergic acid

N

S

CO2H

CH2CNH

O

penicillin G

O OH

OH

NCH3

morphine

Page 27: Benzene and Aromaticity

Designer Drugs

O OH

OH

NCH3

morphine

O OH

OCH3

NCH3

codeine

OOCH3

NCH3

O

oxycodoneoxycontin (slow release)

percocet (w/ acetominophen)

O OAc

OAc

NCH3

heroin

Page 28: Benzene and Aromaticity

Nomenclature

Br NO2

bromobenzene nitrobenzene ethylbenzene

CH2CH3

Page 29: Benzene and Aromaticity

Disubstitutionortho, meta and para

X

X

X

X

X

Xortho meta para

Page 30: Benzene and Aromaticity

Disubstitution Nomenclature

Br

CH2CH2CH3

ortho bromopropylbenzene

NO2

NO2

meta dinitrobenzene

Cl

CH2CH3

para chloroethylbenzene

Page 31: Benzene and Aromaticity

Aromatic Template Names

toluene xylene mesitylene styrene

CH=CH2CH3

CH3CH3

CH3

CH3

CH3

OH NH2OCH3CH(CH3)2

cumene phenol anisole aniline

Page 32: Benzene and Aromaticity

More Common Names

CCH3

O

O

acetophenone benzophenone

SO3H CHO CO2H CN

benzene sulfonic acid benzaldehyde benzoic acid benzonitrile

Page 33: Benzene and Aromaticity

Aromatic Ring as a Substituent

5,7-dimethyl-4-phenyl-1-octene

CH2

Br

trans 1-benzyl-2-bromocycloheptane

Page 34: Benzene and Aromaticity

Name These

d)c)

Cl

Cl

CH3

b)

NO2

CO2H

a)

OCH3

I

CH=CH2

Page 35: Benzene and Aromaticity

d)c)

Cl

Cl

CH3

b)

NO2

CO2H

a)

OCH3

I

CH=CH2

meta nitrobenzoic acid 3,5-dichlorotoluene

4-iodo-2-propylstyrene ortho isopropylanisole


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