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