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