This document discusses aromatic compounds and benzene chemistry. It begins by introducing aromatic hydrocarbons and noting they have different properties than aliphatic hydrocarbons. Benzene, the simplest aromatic hydrocarbon, is described as having posed problems for early chemists to determine its structure. Kekulé proposed benzene has alternating single and double bonds, but this did not explain its chemical behavior. The resonance structure of benzene is able to account for its reactivity. The document continues discussing nomenclature of aromatic compounds with different numbers of substituents on the benzene ring. Characteristic reactions of benzene like halogenation and nitration are also covered. Phenols are introduced as aromatic compounds containing an -OH group

1. By
Dr KHALED ALGARIRI
CAMS- QASSIM UNIVERSITY
October 2020

2. INTRODUCTION
More than 150 years ago, organic chemists realized that yet another class of
hydrocarbons exists, one whose properties are quite different from those of
aliphatic hydrocarbons.
Because some of these new hydrocarbons have pleasant odors, they were
called aromatic compounds. Today we know that not all aromatic
compounds share this characteristic. Some do have pleasant odors, but
some have no odor at all, and others have downright unpleasant odors.

3. Arene A compound containing one or more benzene-like rings.
Aryl group A group derived from an arene by removal of a H atom from an
arene and given the symbol Ar
Benzene is an important compound in both the chemical industry and the
laboratory, but it must be handled carefully. Not only is it poisonous if
ingested in liquid form, but its vapor is also toxic and can be absorbed either
by breathing or through the skin. Long-term inhalation can cause liver damage
and cancer.

4. CHEMSITRY OF BENZENE COMPUND
Benzene, the simplest aromatic hydrocarbon, was discovered in 1825 by Michael
Faraday (1791–1867). Its structure presented an immediate problem to chemists of
the day. Benzene has the molecular formula C6H6, and a compound with so few
hydrogens for its six carbons.
chemists argued, should be unsaturated.But benzene does not behave like an alkene
(the only class of unsaturated hydrocarbons known at that time). Whereas 1-hexene,
for example, reacts instantly with Br2 ,benzene does not react at all with this
reagent. Nor does benzene react with HBr, H2O/H2SO4, or H2, all reagents that
normally add to carbon–carbon double bonds

5. CHEMSITRY OF BENZENE COMPUND
Kekulé’s Structure of Benzene
The first structure for benzene was proposed by Friedrich August Kekulé in 1872 and
consisted of a six-membered ring with alternating single and double bonds, with one
hydrogen bonded to each carbon.
The major objection was its failure to account for the unusual chemical behavior of
benzene. If benzene contains three double bonds, Kekulé’s critics asked, why doesn’t it
undergo reactions typical of alkenes?
Resonance Structure of Benzene

6. NAMES OF AROMATIC COPMPOUNDS
One Substituent
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, including toluene
and styrene
The substituent group derived by loss of an H from benzene is called a
phenyl group, C6H5-, the common symbol for which is Ph-

7. B. Two Substituents
When two substituents occur on a benzene ring, three
isomers are possible.
We locate the substituents either by numbering the atoms
of the ring or by using the locators ortho (o), meta (m), and
para (p).
When one of the two substituents on the ring imparts a special name to the compound (for
example, -CH3, -OH, -NH2, or -COOH), we name the compound as a derivative of that
parent molecule and assume that the substituent occupies ring position number 1.
NOMENCLATURE OF AROMATIC
COPMPOUNDS

8. C. Three or More Substituents
When three or more substituents are present on a benzene ring, specify their locations
by numbers. If one of the substituents imparts a special name, then name the molecule
as a derivative of that parent molecule. If none of the substituents imparts a special
name, then locate the substituents, number them to give the smallest set of numbers,
and list them in alphabetical order before the ending “benzene.”

9. Write names for these compounds.
Strategy
First check to see if one of the substituents on the benzene ring imparts a special name.
If one of them does, then name the compound as a derivative of that parent molecule.
Solution
(a) The parent is toluene, and the compound is 3-iodotoluene or m-iodotoluene.
(b) The parent is benzoic acid, and the compound is 3,5-dibromobenzoic acid.
(c) The parent is aniline, and the compound is 4-chloroaniline or p-chloroaniline.

10. Characteristic Reactions of Benzene and Its
Derivatives?
A.Halogenation
In the presence of an iron catalyst,
chlorine reacts rapidly with benzene to
give chlorobenzene and HCl:
Treatment of benzene with bromine in the presence of FeCl3 results in formation
of bromobenzene and HBr.

11. B. Nitration
When we heat benzene or one of its derivatives with a
mixture of concentrated nitric and sulfuric acids, a nitro -
NO2 group replaces one of the hydrogen atoms bonded
to the ring.
C. Sulfonation
Heating an aromatic compound with concentrated
sulfuric acid results in formation of an arenesulfonic acid,
all of which are strong acids, comparable in strength to
sulfuric acid.

12. PHENOLS
A phenol is an organic compound in which an -OH
group is attached to a carbon atom that is part of
an aromatic carbon ring system.

13. Nomenclature for Phenols
The IUPAC rules for naming phenols are simply extensions of the rules used to
name benzene derivatives with hydrocarbon or halogen substituents .The parent
name is phenol. Ring numbering always begins with the hydroxyl group and
proceeds in the direction that gives the lower number to the next carbon atom
bearing a substituent.
The numerical position of the hydroxyl group is not specified in the name because it
is 1by definition.

14. Methyl and hydroxy derivatives of phenol have
IUPAC-accepted common names.Methylphenols
are called cresols. The name cresol applies to
all three isomeric methylphenols.
For hydroxyphenols, each of the three isomers has a different common name

15. Physical and Chemical Properties of
Phenols
1. Phenols are generally low-melting solids or oily liquids at
room temperature.
2. Most of them are only slightly soluble in water.
3. Many phenols have antiseptic and disinfectant properties.

16. The similarities and differences between
the Phenols and Alcohols
1. Both alcohols and phenols are flammable.
2. Dehydration is a reaction of alcohols but not of phenols; phenols
cannot be dehydrated.
3. Both 1° and 2° alcohols are oxidized by mild oxidizing agents.
Tertiary (3°) alcoholsand phenols do not react with the oxidizing agents
that cause 1° and 2° alcohol oxidation.Phenols can be oxidized by
stronger oxidizing agents.
4. Both alcohols and phenols undergo halogenation in which the
hydroxyl group is
replaced by a halogen atom in a substitution reaction

17. Acidity of Phenols
 Phenols are weak acids, with pKa values of approximately 10 .
 Most phenols are insoluble in water, but they react with strong bases,
such as NaOH and KOH, to form water-soluble salts.
 Most phenols are such weak acids that they do not react with
weak bases such as sodium bicarbonate; that is, they do not
dissolve in aqueous sodium bicarbonate.

18. Phenols and Chemistry of life
 Dilute (2%) solutions of phenol have long been used as antiseptics. Concentrated
phenol solutions, however, can cause severe skin burns. Today, phenol has been
largely replaced by more effective phenol derivatives such as 4-hexylresorcinol. The
compound 4-hexylresorcinol is an ingredient in many mouthwashes and throat
lozenges.
 The phenol derivatives o-phenylphenol and 2-benzyl-4-chlorophenol are the active
ingredients in Lysol, a disinfectant for walls, floors, and furniture in homes and
hospitals.
 A number of phenols found in plants are used as flavoring agents and/or
antibacterials. Included among these phenols a

19.  A number of phenols possess antioxidant activity. An antioxidant is a substance that
protects other substances from being oxidized by being oxidized itself in preference to
the other substances. An antioxidant has a greater affinity for a particular oxidizing
agent than do the substances the antioxidant is “protecting”; the antioxidant, therefore,
reacts with the oxidizing agent first. Many foods sensitive to air are protected from
oxidation through the use of phenolic antioxidants. Two commercial phenolic
antioxidant food additives are BHA (butylated hydroxy anisole) and BHT (butylated
hydroxy toluene)
Phenols and Chemistry of life

20. Vanillin, which gives vanilla its flavor, is extracted from the dried
seed pods of the vanilla orchid. Natural supplies of vanillin are
inadequate to meet demand for this flavoring agent. Synthetic
vanillin is produced by oxidation of eugenol.
Phenols and Chemistry of life

21. Thymol, obtained from the herb thyme,
possesses both flavorant and antibacterial
properties. It is used as an ingredient in several
mouthwash formulations.
Eugenol is responsible for the flavor of cloves. Dentists
traditionally used clove oil as an antiseptic because of
eugenol’s presence; they use it to a limited extent even
today. Isoeugenol, which differs in structure from eugenol
only in the location of the double bond in the hydrocarbon
side chain, is responsible for the odor associated with
nutmeg
Phenols and Chemistry of life

22. Capsaicin, for Those Who Like It Hot
Capsaicin, the pungent principle from the fruit of
various species of peppers (Capsicum and
Solanaceae), was isolated in 1876, and its structure
was determined in 1919. Capsaicin contains both a
phenol and a phenol ether.

23. The inflammatory properties of capsaicin are well
known; the human tongue can detect as little as one drop in 5 L of water. We all know of
the burning sensation in the mouth and sudden tearing in the eyes caused by a good
dose of hot chili peppers. For this reason, capsaicin containing extracts from these
flaming foods are used in sprays to ward off dogs or other animals that might nip at your
heels while you are running or cycling.

24. Home workDiscuss the following
1-Hybridization of carbon; properties of sp3 , sp2 , sp .
2-Carbon as basic element of life: Electronic structure of carbon and
valency
3- Covalent bonds of carbon; sigma bonds and pi bonds .
4-Hybridization of carbon in simple organic compounds; CH4,
C2H4,C2H2 .
5- Delocalization and pi bonds; C6H6
Deadline is this Thrusday 29 October 2020

25. Thank you for
your attention!