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Chemistry 2100
Chapter 13
Discovering Aromatics
C6H6 Ladenburg 1878
Dewar 1867CH3C C C C CH3
CHH2C C C CH CH2 Br 2 / Fe
(- HBr )C6H6 C6H5Br
Br 2 / Fe
(- HBr )C6H4Br2
1.54 Å 1.33 Å 1.39 Å
CH3 CH3 CH2 CH2 C6H6
Aromatics H H
H
H
H
H H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H H
H H
H H
Resonance
H H
H H
H H
Resonance
H H
H H
H H
Resonance
H H
H H
H H
Resonance
H H
H H
H H
Resonance
H H
H H
H H
Resonance
H H
H H
H H
Resonance
H H
H H
H H
Resonance
Resonance
Graphene
Carbon Nanotubes
Nomenclature for Arenes
• Many common names retained• PAH
PhenanthreneAnthraceneNaphthalene Benzo[a]pyrene
Nomenclature
• Monosubstituted alkylbenzenes are named as derivatives of benzene; for example, ethylbenzene.
• The IUPAC system retains certain common names for several of the simpler monosubstituted alkylbenzenes.
Nomenclature
– The common names for these monosubstituted benzenes are also retained
– Phenyl group (C6H5- or Ph-): The substituent group derived by removal of an H from benzene.
Nomenclature
When two substituents occur on a benzene ring, three isomers are possible; they may be located by:– numbering the atoms of the ring or – using the locators ortho (o), meta (m),
and para (p).
Aromatic Reactions
Reactions of Benzene
By far the most characteristic reaction of aromatic compounds is substitution at a ring carbon.– This reaction is called aromatic substitution.– Some groups that can be introduced directly on
the ring are the halogens, the nitro (-NO2) group, and the sulfonic acid (-SO3H) group.
Halogenation:
20
Phenols
The functional group of a phenol is a hydroxyl ( -OH) group bonded to a benzene ring.– Name substituted phenols either as
derivatives of phenol or by common names.
21
Noteworthy Phenols hexachlorophene
OHCl
Cl Cl
CH2
Cl
ClCl
HO eugenol
HO
CH3O hexylresorcinol
OH
HO OH
Cl
O
CH3HO
OHOH
HN(CH3)2
OH
O
CONH2
aureomycin
O
HO
tetrahydrocannabinol
Phenol Acidity
>>
acids > thiols ~ phenols > water ~ alcohols
C OHCH3
O
OH CH3 OH
Acidity:
acids > phenols ~ thiols > water ~ alcohols
Ka % ionized [H3O+], M pH
~1 107 ~100 ~0.1 1.00
1.8 10–5 1.3 1.3 10–3 2.88
3.3 10–10 0.0036 3.6 10–6 5.44
2.5 10–11 0.0016 1.6 10–6 5.80
1.3 10–16 0.0001 1.0 10–7 7.00
HCl
HOAc
PhOH
EtSH
EtOH
HOH
Comparative acidities of 0.1 M aqueous solutions of representative acids HA
1.8 10–16 0.0001 1.0 10–7 7.00
Phenols as AntioxidantsAutoxidation
CH2CH=CH-CHH
CH2CH=CH-CHSection of a fatty
acid hydrocarbon chainA carbon radical
lightor heat
CH2CH=CH-CH-CH2
O-O-H
A hydroperoxide
CH2CH=CH-CHO-O
CH2CH=CH-CH
H+
+ CH2CH=CH-CH A new carbon radical
Section of a new fattyacid hydrocarbon chain
CH2CH=CH-CH O-O CH2CH=CH-CHO-O
A hydroperoxy radical
+Oxygen is adiradical
Natural Phenolic Antioxidants
HO
O
CH3
CH3CH3CH3
CH3
CH3CH3 CH3
Vitamin E ( tocopherol)Vitamin E (-tocopherol) OH
OH
HO
Resveratrol
Man-made Phenolic Antioxidants
OH
CH3
BHT
OH
OCH3
BHA
methyl paraben
OC
OCH3
OH
Phenols as… Weapons?
CH2 CH NH2
COOH
phenylalanine
CH2 CH NH2
COOH
phenylalanine
[O]
tyrosine
CH2 CH NH2
COOH
HO
CH2 CH NH2
COOH
phenylalanine
[O]
L-DOPA
CH2 CH NH2
COOH
HO
HO
[O]
tyrosine
CH2 CH NH2
COOH
HO
CH2 CH NH2
COOH
phenylalanine
[O]
L-DOPA
CH2 CH NH2
COOH
HO
HO
[O]
tyrosine
CH2 CH NH2
COOH
HO
CH2 CH NH2
COOH
phenylalanine
[O]
L-DOPA
CH2 CH NH2
COOH
HO
HO
[O]
tyrosine
CH2 CH NH2
COOH
HO
CH2 CH NH2
COOH
phenylalanine -CO2
CH2 CH2 NH2
HO
HO
dopamine
[O]
L-DOPA
CH2 CH NH2
COOH
HO
HO norepinephrine
CH CH2 NH2
HO
HO
OH
[O]
[O]
tyrosine
CH2 CH NH2
COOH
HO
CH2 CH NH2
COOH
phenylalanine -CO2
CH2 CH2 NH2
HO
HO
dopamine
epinephrine
"CH3"CH CH2 NH
HO
HO
OH
CH3
[O]
L-DOPA
CH2 CH NH2
COOH
HO
HO norepinephrine
CH CH2 NH2
HO
HO
OH
[O]
[O]
tyrosine
CH2 CH NH2
COOH
HO
CH2 CH NH2
COOH
phenylalanine -CO2
CH2 CH2 NH2
HO
HO
dopamine
epinephrine
"CH3"CH CH2 NH
HO
HO
OH
CH3
[O]
L-DOPA
CH2 CH NH2
COOH
HO
HO norepinephrine
CH CH2 NH2
HO
HO
OH
[O]
[O]
tyrosine
CH2 CH NH2
COOH
HO
CH2 CH NH2
COOH
phenylalanine -CO2
CH2 CH2 NH2
HO
HO
dopamine
CH CH NH
"phenethylamine"
CH CH NH
ephedrine (ephedra) / pseudoephedrine
OH
CH3 CH3
ephedrine (ephedra) / pseudoephedrine
OH
CH3
CH CH NH
CH3
CH CH NH 2
CH3
methylenedioxymethamphetamine / MDMA / Ecstacy
CH3
CH CH NH 2
O
O
CH3
methylenedioxymethamphetamine / MDMA / Ecstacy
CH3
CH CH NH 2
O
O
CH3
methylenedioxymethamphetamine / MDMA / Ecstacy
CH3
CH CH NH 2
O
O
CH3
methylenedioxymethamphetamine / MDMA / Ecstacy
CH3
Organic Food Dye: Carminic Acid
carminic acid
O
O
OH
COOH
OH
OH
HO
HO
OH
Aromatic Heterocycles
nicotineniacin (B3) / nicotinamide
thiamine (B1)
N
NCH3
N
C NH2
O CH3
NH2
CH3
N
N
CH2
N
S
CH2CH2OHCl
caffeine(theobromine)
CH3
N
N
CH3
N
N(H) CH3
O
O• •
••
Heterocycles store life’s information
(U) T = A
N
N
O
O
H
(H) CH3
Sugar
(U) T = A
Sugar
H
H N N
NN
N
N
N
O
O
H
(H) CH3
Sugar
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