benzene and aromaticity
DESCRIPTION
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 PresentationTRANSCRIPT
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Benzene and Aromaticity
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Bonding in Benzene
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Proposed Benzene Structures
Dewar benzene Ladenburg benzene
Kekule benzene
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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
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Other Conjugated Hydrocarbon RingsAnnulenes
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Hhyd Data Illustrates Stability
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Benzene Representations
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Molecular Orbitals of Benzene
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M.O.’s of Cyclobutadiene
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1 3
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6 Electrons is Stable4 or 8 Electrons is not
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Huckel’s Rule: 4N + 2
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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
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Naphthalene
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Pyridine, an Aromatic Heterocycle
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Pyridine as a Base
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Pyrrole
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Pyrrole as a Base
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Other Aromatic Heterocycles
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Cyclopentadiene as an AcidpKa = 16
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Cyclopentadienyl ion:One is Aromatic, one is Antiaromatic
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Resonance Depictions of the Ions
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Tropylium Ion
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Aromatic?
c)b)a)NH
BHO
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Aromatic, Anti-Aromatic or Nonaromatic?
c)
N
N
H
H
b) a)
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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
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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
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Nomenclature
Br NO2
bromobenzene nitrobenzene ethylbenzene
CH2CH3
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Disubstitutionortho, meta and para
X
X
X
X
X
Xortho meta para
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Disubstitution Nomenclature
Br
CH2CH2CH3
ortho bromopropylbenzene
NO2
NO2
meta dinitrobenzene
Cl
CH2CH3
para chloroethylbenzene
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Aromatic Template Names
toluene xylene mesitylene styrene
CH=CH2CH3
CH3CH3
CH3
CH3
CH3
OH NH2OCH3CH(CH3)2
cumene phenol anisole aniline
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More Common Names
CCH3
O
O
acetophenone benzophenone
SO3H CHO CO2H CN
benzene sulfonic acid benzaldehyde benzoic acid benzonitrile
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Aromatic Ring as a Substituent
5,7-dimethyl-4-phenyl-1-octene
CH2
Br
trans 1-benzyl-2-bromocycloheptane
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Name These
d)c)
Cl
Cl
CH3
b)
NO2
CO2H
a)
OCH3
I
CH=CH2
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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