Aromatic

Compounds

Good Aromati

cs

cinnamon

CINNAMALDEHYDE

CH CH – C – H ═

O║

coffee

CAFFEINE

O║

O║

CH3

3HC

CH3

N

NN

N

vanillaOH

OCH3

H – C ═ OVANILLIN

Filipino BBQ goodness: puto (rice muffins)

                                                                                                                                                      

aniseed/aniseOCH

3

CH ═ CH – CH3ANETHOLE

clovesOH

OCH3

CH2 – CH ═ CH2EUGENOL

wintergreen

OH

O║C – O – CH3

METHYL SALICYLATE

chamomile

COUMARIN

O O║

Bad Aroma

tics

benzene

BENZENE

naphthalene

NAPHTHALENE

burnt meat

PHENANTHRENE

smoke belchers

BENZOPYRENE

smoke belchers

PYRENE CORONENE

cigarettesBENZANTHRACENE

DIBENZ ANTHRACENE

cigarettesN

NO

N

NITROSONORNICOTINE

Lets try to find out the missing

piece of the puzzle that

leads to that occurrence…

HISTORY

“ Let us learn to dream,

gentlemen, and then perhaps we shall learn the truth.”

- 1890 Kekulé -

Some of the early researchers in organic

chemistry became intrigued by fragrant oils that could be extracted from certain plants. The compounds

responsible for the aromas, had similar chemical

properties. As a result, they were grouped together and

called AROMATICS COMPOUNDS.

As more and more aromatic compounds were isolated and

studied, chemist gradually realized that aromatic

contained six carbon atoms and had low hydrogen – to –

carbon ratios (relative to other hydrocarbon). They also realized that the term

aromatic was not always accurate. Because there are

many fragrant compounds do not have aromatic properties.

1825 – Michael Faraday

discovered BENZENE in whale oil.

When BENZENE was found to have the formula C6H6, scientist was puzzled.

They tried unsuccessfully to draw a straight – line structure

for BENZENE.

BENZENE’s possible structures

CH3 — C ≡ C ─ C ≡ C — CH3

CH2 ═ CH ─ C ≡ C ─ CH ═ CH2

2,4 – hexadiyne

1,5 – hexadien – 3 – yne

Kekule was to say later that he must have dozed off at this point. In his dream the black balls of carbon turned into black imps with forked tails that began racing around the room and would soon be upsetting the apparatus of the laboratory. He was ready to run the rascals out. Then, almost suddenly, the confusion

died away as each imp grabbed the tail of the one ahead of him, the six forming a whirling circle. One

hand of each imp held a tail, the other a white handkerchief--and they waved to him as the group

whirled by. He said that he came awake with a start, realizing that the imps were acting out the formula for benzene. As his hand grabbed the sketching

pencil, the imps were back to black balls again and the handkerchiefs had changed to hydrogen atoms.

How simple the arrangement turned out to be. “The carbon atoms of benzene form

a ring."

1858 – Friedrich August von Stradonitz Kekulé.

Suggested that the six carbon atoms formed a cyclic

structure having three sets of alternating double bonds.

1865 – Kekulé proposed that BENZENE had two structural

formulas and that is alternated between them.

1931 – Linus Pauling

To help explain molecules like benzene, he proposed resonance theory. (Pauling

also gave us hybrid orbitals, electronegativity, and valence bond theory).That gave birth to the modern structure of

BENZENE.

Modern benzene structure

Nomenclature

Rule # 1•When a single hydrogen of the benzene ring is replaced, the

compound can be named as a derivative

of benzene.

Examples:CH2CH3

ethylbenzene

Br

bromobenzene

Clchlorobenzene

NO2

nitrobenzene

Rule # 2•A number of benzene

derivatives are known by common names that are also IUPAC – accepted

and are used preferentially over other

possibilities.

Examples:CH3

Toluene

OH

Phenol

NH2

Aniline

C — OH

║O

Benzoic Acid

O ║ C – CH3

acetophenon

e O ║ C benzopheno

ne

EXAMPLES O ║ C – H

benzaldehyd

e

Rule # 3• Compounds formed by replacing a hydrogen of

benzene with more complex hydrocarbon group can be named by designating the

benzene ring as substituent.• We called them phenyl

group. • benzyl

Examples:CH3CHCH ═ CH2

3 – phenyl – 1 – butene

CH3 — C — C — C — CH3

ا ا ااا ا

Br

Br3HC

3HC

2,2 – dibromo – 4,4 – dimethyl – 3,3 – diphenylpentane

CH2OH

Cl 2 – benzyl – 4 – chlorophenol

Rule # 4•When two groups are attached to a benzene

ring, three isomeric structures are possible. They can be designated

by the prefixes ortho (o), meta (m), and para

(p):

Examples:Cl

Br

O - bromochlorobenzene

CO2H

NO2

m – nitrobenzoic acid

CH3

Clp - chlorotoluene

Examples:CH3 CH3 CH3

CH3

CH3

CH31,2 – dimethylbenzene

O – xylene 1,3 - dimethylbenzene

m – xylene

1,4 - dimethylbenzenep - xylene

Rule # 5• When two or more groups are attached to a benzene ring, their

positions can be indicated by numbering the carbon atoms of

the ring so as to obtain the lowest possible numbers for the

attachment positions. • Group that comes first in

alphabetical order is given the lower number.

Examples:Br

Cl

I

O2N NO2

OH

NO2

CH3

NO2

Br

1 – bromo – 2 – chloro – 4 – iodobenzene

2,4,6 – trinitrophenol

3 – bromo – 5 - nitrotoluene

Examples:NO2

NO2 NO21,3,5 –

trinitrobenzene

CH3

NO2

2ON NO2

2,4,6 - trinitrotoluene

TNT

Preparation• Major sources of aromatic

compounds are petroleum and coal tar – (a sticky, dark – colored material derived from coal.

• Natural sources• Can be synthesize

synthetically

PhysicalProperties

Physical Properties• Similar to those of

ALKANES & ALKENES• Non – Polar• Insoluble in water (hydrophobic)

• Flammable• Low density in water

Chemical

Properties

Benzene Reactions•Halogenation

•Nitration•Sulfonation•Alkylation

Industrial Application

s

Medicine

Medicine

Antiseptic

Consumer Products

Disinfectant

Synthetic Fiber

Plastic

Preservatives

Dyes

Fuel Additives

– fin –