After studying this Unit, you will be
able to
name alcohols, phenols and
ethers according to the IUPAC
system of nomenclature;
discuss the reactions involved in
the preparation of alcohols from
alkenes, aldehydes, ketones and
carboxylic acids;
discuss the reactions involved in
the preparation of phenols from
haloarenes, benzene sulphonic
acids, diazonium salts and
cumene;
discuss the reactions for
preparation of ethers from
(i) alcohols and (ii) alkyl halides
and sodium alkoxides/aryloxides;
correlate physical properties of
alcohols, phenols and ethers with
their structures;
discuss chemical reactions of the
three classes of compounds on
the basis of their functional
groups.
Objectives
Alcohols, phenols and ethers are the basic compounds for the
formation of detergents, antiseptics and fragrances, respectively.
11
Unit
Unit
Unit
Unit
Unit
11
Alcohols
Alcohols
Alcohols
Alcohols
Alcohols
,,
,,
,
PhenolsPhenols
PhenolsPhenols
Phenols
andand
andand
and
EE
EE
E
therther
therther
ther
ss
ss
s
AlcoholsAlcohols
AlcoholsAlcohols
Alcohols
,,
,,
,
PhenolsPhenols
PhenolsPhenols
Phenols
andand
andand
and
EE
EE
E
therther
therther
ther
ss
ss
s
You have learnt that substitution of one or more
hydrogen atom(s) from a hydrocarbon by another atom
or a group of atoms result in the formation of an entirely
new compound having altogether different properties
and applications. Alcohols and phenols are formed
when a hydrogen atom in a hydrocarbon, aliphatic and
aromatic respectively, is replaced by –OH group. These
classes of compounds find wide applications in industry
as well as in day-to-day life. For instance, have you
ever noticed that ordinary spirit used for polishing
wooden furniture is chiefly a compound containing
hydroxyl group, ethanol. The sugar we eat, the cotton
used for fabrics, the paper we use for writing, are all
made up of compounds containing –OH groups. Just
think of life without paper; no note-books, books, news-
papers, currency notes, cheques, certificates, etc. The
magazines carrying beautiful photographs and
interesting stories would disappear from our life. It
would have been really a different world.
An alcohol contains one or more hydroxyl (OH)
group(s) directly attached to carbon atom(s), of an
aliphatic system (CH
3
OH) while a phenol contains –OH
group(s) directly attached to carbon atom(s) of an
aromatic system (C
6
H
5
OH).
The substitution of a hydrogen atom in a
hydrocarbon by an alkoxy or aryloxy group
(R–O/Ar–O) yields another class of compounds known
as ‘ethers’, for example, CH
3
OCH
3
(dimethyl ether). You
may also visualise ethers as compounds formed by
2020-21
324Chemistry
substituting the hydrogen atom of hydroxyl group of an alcohol or
phenol by an alkyl or aryl group.
In this unit, we shall discuss the chemistry of three classes of
compounds, namely — alcohols, phenols and ethers.
Monohydric alcohols may be further classified according to the
hybridisation of the carbon atom to which the hydroxyl group is
attached.
(i) Compounds containing
3
C OH
sp
bond: In this class of alcohols,
the –OH group is attached to an sp
3
hybridised carbon atom of an
alkyl group. They are further classified as follows:
Primary, secondary and tertiary alcohols: In these three types of
alcohols, the –OH group is attached to primary, secondary and
tertiary carbon atom, respectively as depicted below:
Allylic alcohols: In these alcohols, the —OH group is attached to
a sp
3
hybridised carbon adjacent to the carbon-carbon double
bond, that is to an allylic carbon. For example
Benzylic alcohols: In these alcohols, the —OH group is attached
to a sp
3
—hybridised carbon atom next to an aromatic ring. For
example.
The classification of compounds makes their study systematic and
hence simpler. Therefore, let us first learn how are alcohols, phenols
and ethers classified?
Alcohols and phenols may be classified as mono–, di–, tri- or
polyhydric compounds depending on whether they contain one, two,
three or many hydroxyl groups respectively in their structures as
given below:
11.1 11.1
11.1 11.1
11.1
ClassificationClassification
Classification
Classification
Classification
11.1.1 Alcohols—
Mono, Di,
Tri or
Polyhydric
alcohols
Monohydric
Dihydric
Trihydric
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325 Alcohols, Phenols and Ethers
Allylic and benzylic alcohols may be primary, secondary or tertiary.
(ii) Compounds containing
2
C OH
sp
bond: These alcohols contain
—OH group bonded to a carbon-carbon double bond, i.e., to a
vinylic carbon or to an aryl carbon. These alcohols are also known
as vinylic alcohols.
Vinylic alcohol: CH
2
= CH – OH
11.1.3 Ethers
CH
3
C
CH OH
2
CH
3
CH
3
(i)
H C
2
CH
CH OH
2
(ii)
CH
3
CH
2
CH OH
2
(iii)
CH
OH
CH
3
(iv)
CH
2
OH
CH
CH
3
(v)
CH
OH
CH
C
CH
3
CH
3
(vi)
11.1 Classify the following as primary, secondary and tertiary alcohols:
11.2 Identify allylic alcohols in the above examples.
Intext QuestionsIntext Questions
Intext QuestionsIntext Questions
Intext Questions
11.2 Nomenclature11.2 Nomenclature
11.2 Nomenclature11.2 Nomenclature
11.2 Nomenclature
(a) Alcohols: The common name of an alcohol is derived from the
common name of the alkyl group and adding the word alcohol to it.
For example, CH