Alcohols, Phenols and Ethers

Alcohols are formed when a hydrogen atom in a hydrocarbon, aliphatic is replaced by

OH group. Examples: CH3OH, C2

Phenols are formed when a hydrogen atom in a hydrocarbon,

OH group. Example: C6H5OH

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

(dimethyl ether).

Classificati

Monohydric: CH3OH Methyl alcohol,

Phenol

Dihydric:

Ethylene Glycol

Trihydric:

Class- XII

Chemistry

Chapter-11

Alcohols, Phenols and Ethers

Alcohols

Alcohols are formed when a hydrogen atom in a hydrocarbon, aliphatic is replaced by

2H5OH

Phenols

Phenols are formed when a hydrogen atom in a hydrocarbon, aromatic is replaced by

Ethers

The substitution of a hydrogen atom in a hydrocarbon by an alkoxy or aryloxy group (R

O) yields another class of compounds known as ‘ethers’, for example, CH

Classification of Alcohols and Phenols

OH Methyl alcohol, C2H5OH-Ethyl alcohol

Ethylene Glycol

Alcohols are formed when a hydrogen atom in a hydrocarbon, aliphatic is replaced by –

aromatic is replaced by –

The substitution of a hydrogen atom in a hydrocarbon by an alkoxy or aryloxy group (R–

O) yields another class of compounds known as ‘ethers’, for example, CH3OCH3

Glycerol

Classification according to the hybridisation of the carbon atom to which the hydroxyl

group is attached.

(i) Compounds containing C

Alkyl Alcohol

Primary, secondary and tertiary alcohols

Allylic alcohols:

Benzylic alcohols:

Glycerol

Classification according to the hybridisation of the carbon atom to which the hydroxyl

Compounds containing Csp3-OH bond:

Primary, secondary and tertiary alcohols

Classification according to the hybridisation of the carbon atom to which the hydroxyl

(ii) Compounds containing Csp2- OH bond

Classification of Ethers

Simple or symmetrical if the alkyl or aryl groups attached to the oxygen atom are the

same. Example Diethyl ether, C2H5OC2H5

Mixed or unsymmetrical if the two groups are different.

C2H5OCH3 and C2H5OC6H5 are unsymmetrical ethers.

Preparation of Alcohols

1.From alkenes:

(i) By acid catalysed hydration:

Mechanism The mechanism of the reaction involves the following three steps:

Step 1:

Protonation of alkene to form carbocation by electrophilic attack of H3O+.

(ii)By hydroboration–oxidation:

2.From carbonyl compounds

(i) By reduction of aldehydes and ketones

oxidation:

2.From carbonyl compounds

By reduction of aldehydes and ketones:

The usual catalyst is a finely divided metal such as platinum(Pt), palladium(Pd) or

nickel (Ni). It is also prepared by treating aldehydes and ketones with sodium

borohydride (NaBH4) or lithium aluminium hydride (LiAlH4)

(iii) By reduction of carboxylic acids and esters:

3. From Grignard reagents:

Alcohols are produced by the reaction of Grignard reagents with aldehydes and

ketones.

Preparation of Phenols

1. From haloarenes:

Chlorobenzene is fused with NaOH at 623K and 3

is obtained by acidification of sodium phenoxide so produced.

2. From benzene sulphonic acid:

Benzene is sulphonated with oleum and benzene sulphonic acid so formed is

converted to sodium phenoxide on heating with molten sod

Acidification of the sodium salt gives phenol.

Alcohols are produced by the reaction of Grignard reagents with aldehydes and

Chlorobenzene is fused with NaOH at 623K and 320 atmospheric pressure. Phenol

is obtained by acidification of sodium phenoxide so produced.

From benzene sulphonic acid:

Benzene is sulphonated with oleum and benzene sulphonic acid so formed is

converted to sodium phenoxide on heating with molten sodium hydroxide.

Acidification of the sodium salt gives phenol.

Alcohols are produced by the reaction of Grignard reagents with aldehydes and

20 atmospheric pressure. Phenol

Benzene is sulphonated with oleum and benzene sulphonic acid so formed is

ium hydroxide.

3. From diazonium salts

4. From cumene

From cumene Phenol is manufactured from the hydrocarbon, cumene. Cumene

(isopropyl benzene) is oxidised in the presence of air to cumene hydroperoxide. It is

converted to phenol and acetone by treating it with dilute acid. Acetone, a by-

product of this reaction, is also obtained in large quantities by this method.

Physical Properties of Alcohol and Phenol

Boiling Points

The boiling points of alcohols and phenols increase with increase in the number of

carbon atoms (increase in van der Waals forces). In alcohols, the boiling points

decrease with increase of branching in carbon chain (because of decrease in van

der Waals forces with decrease in surface area).

Boiling points of alcohols and phenols are higher in comparison to other classes of

compounds, namely hydrocarbons, ethers, haloalkanes and haloarenes of

comparable molecular masses.

The high boiling points of alcohols are mainly due to the prese

hydrogen bonding in them which is lacking in ethers and hydrocarbons

Solubility

Solubility of alcohols and phenols in water is due to their ability to form

hydrogen bondwith water molecules.

Chemical Properties of A

Alcohols are versatile compounds. They react both as nucleophiles and electrophiles.

i) The bond between O–

(a) Reactions involving cleavage of O

1. Acidic nature of alcohols and phenols:

Acidic nature of alcohols:

The high boiling points of alcohols are mainly due to the presence of intermolecular

hydrogen bonding in them which is lacking in ethers and hydrocarbons

Solubility of alcohols and phenols in water is due to their ability to form

water molecules.

cal Properties of Alcohol and Phenol

Alcohols are versatile compounds. They react both as nucleophiles and electrophiles.

–H is broken when alcohols react as nucleophiles.

Reactions involving cleavage of O–H bond

Acidic nature of alcohols and phenols:

nce of intermolecular

hydrogen bonding in them which is lacking in ethers and hydrocarbons.

Solubility of alcohols and phenols in water is due to their ability to form

Alcohols are versatile compounds. They react both as nucleophiles and electrophiles.

H is broken when alcohols react as nucleophiles.

Alcohols react with sodium to form a salt (sodium

Acidic nature of phenols:

Reason

The hydroxyl group, in phenol is directly attached to the sp2 hybridised carbon

of benzene ring which acts as an ele

charge distribution in phenol molecule, as depicted in its resonance structures,

causes the oxygen of

to form a salt (sodium alkoxide) and hydrogen gas

The hydroxyl group, in phenol is directly attached to the sp2 hybridised carbon

of benzene ring which acts as an electron withdrawing group.

charge distribution in phenol molecule, as depicted in its resonance structures,

causes the oxygen of –OH group to be positive.

alkoxide) and hydrogen gas

The hydroxyl group, in phenol is directly attached to the sp2 hybridised carbon

ctron withdrawing group. Due to this, the

charge distribution in phenol molecule, as depicted in its resonance structures,

(iv) Comparison between acidity of phenol with ethanol.

Phenols are stronger acids than

(i)The reaction of phenol with aqueous sodium hydroxide indicates that phenols are

stronger acids than alcohols and water.

(ii) The ionisation of an alcohol and a phenol

Due to the higher electronegativity of sp2 hybridised carbon of p

attached, electron density decreases on oxygen. This increases the polarity of O

and results in an increase in ionisation of phenols than that of alcohols.

(iii) The stabilities of alkoxide and phenoxide ions

In alkoxide ion, the negative charge is localised on oxygen while in phenoxide ion, the

charge is delocalised. The delocalisation of negative charge makes phenoxide ion more

stable and favours the ionisation of phenol.

omparison between acidity of phenol with ethanol.

Phenols are stronger acids than alcohols because:

(i)The reaction of phenol with aqueous sodium hydroxide indicates that phenols are

stronger acids than alcohols and water.

(ii) The ionisation of an alcohol and a phenol

Due to the higher electronegativity of sp2 hybridised carbon of phenol to which

attached, electron density decreases on oxygen. This increases the polarity of O

and results in an increase in ionisation of phenols than that of alcohols.

(iii) The stabilities of alkoxide and phenoxide ions:

the negative charge is localised on oxygen while in phenoxide ion, the

charge is delocalised. The delocalisation of negative charge makes phenoxide ion more

stable and favours the ionisation of phenol.

(i)The reaction of phenol with aqueous sodium hydroxide indicates that phenols are

henol to which –OH is

attached, electron density decreases on oxygen. This increases the polarity of O–H bond

and results in an increase in ionisation of phenols than that of alcohols.

the negative charge is localised on oxygen while in phenoxide ion, the

charge is delocalised. The delocalisation of negative charge makes phenoxide ion more

2. Esterification

Alcohols and phenols react with ca

form esters.

Alcohols react with carboxylic acids to form esters

The reaction with carboxylic acid and acid anhydride is carried out in the presence of a

small amount of concentrated sulphuric acid. The

water is removed as soon as it is formed

Alcohols react with acid chlorides to form esters

The reaction with acid chloride is carried out in the presence of a base (pyridine) so as to

neutralise HCl which is formed during the reaction. It shifts the equilibrium to the right

hand side.

Phenols react acid anhydrides to form esters

Alcohols and phenols react with carboxylic acids, acid chlorides and acid anhydrides to

Alcohols react with carboxylic acids to form esters

The reaction with carboxylic acid and acid anhydride is carried out in the presence of a

small amount of concentrated sulphuric acid. The reaction is reversible, and therefore,

water is removed as soon as it is formed

Alcohols react with acid chlorides to form esters.

The reaction with acid chloride is carried out in the presence of a base (pyridine) so as to

rmed during the reaction. It shifts the equilibrium to the right

Phenols react acid anhydrides to form esters

rboxylic acids, acid chlorides and acid anhydrides to

The reaction with carboxylic acid and acid anhydride is carried out in the presence of a

reaction is reversible, and therefore,

The reaction with acid chloride is carried out in the presence of a base (pyridine) so as to

rmed during the reaction. It shifts the equilibrium to the right-

Phenols react with carboxylic acids to form esters

Phenols react with acid chlorides to form esters

Acetylation (formation of Aspirin

The introduction of acetyl (CH3CO) group in alcohols or phenols is known as acetylation.

Acetylation of salicylic acid produces aspirin.

(b) Reactions involving cleavage of carbon

1. Reaction with hydrogen halides

halides.

Phenols react with carboxylic acids to form esters

henols react with acid chlorides to form esters

irin)

The introduction of acetyl (CH3CO) group in alcohols or phenols is known as acetylation.

Acetylation of salicylic acid produces aspirin.

(b) Reactions involving cleavage of carbon – oxygen (C–O) bond in alcohols

Reaction with hydrogen halides: Alcohols react with hydrogen halides to form alkyl

The introduction of acetyl (CH3CO) group in alcohols or phenols is known as acetylation.

O) bond in alcohols

Alcohols react with hydrogen halides to form alkyl

ROH + HX → R–X + H2O

Lucas test

Lucas test is used to differentiate and categorize primary, secondary and tertiary alcohols

using a solution of anhydrous zinc chloride (ZnCl2) in concentrated hydrochloric acid (HCl).

This solution is commonly referred to as the Lucas reagent.

Primary

Alcohol

The solution remains colourless unless it is subjected to

heat. The solution forms an oily layer when heated.

Example: 1-Pentanol.

Secondary

Alcohol

The solution turns turbid and forms an oily layer in three to

five minutes (varies based on the solubility). Example: 2-

Pentanol.

Tertiary

Alcohol

The solution turns turbid and forms an oily layer

immediately. Example: 2-methyl-2-butanol.

2. Reaction with phosphorus trihalides: Alcohols are converted to alkyl bromides by

reaction with phosphorus tribromide.

3. Dehydration: Alcohols undergo dehydration (removal of a molecule of water) to form

alkenes on treating with a protic acid e.g., concentrated H2SO4 or H3PO4, or catalysts such

as anhydrous zinc chloride or alumina.

Thus, the relative ease of dehydration of alcohols follows the following order:

Tertiary

Mechanism of Dehydration of alcohols:

5. Oxidation: Oxidation of alcohols involves the formation of a carbon oxygen double

bond with cleavage of an O

Thus, the relative ease of dehydration of alcohols follows the following order:

Tertiary >Secondary > Primary

Mechanism of Dehydration of alcohols:

: Oxidation of alcohols involves the formation of a carbon oxygen double

bond with cleavage of an O-H and C-H bonds. Such a cleavage and formation of

Thus, the relative ease of dehydration of alcohols follows the following order:

: Oxidation of alcohols involves the formation of a carbon oxygen double

H bonds. Such a cleavage and formation of

bonds occur in oxidation reactions. These are also known as dehydrogenation

reactions as these involve loss of dihydrogen from an alcohol molecule.

Strong oxidising agents: KMnO4

Mild oxidising agents: CrO3 in anhydrous medium, pyridinium chlorochromate (PCC), a

complex of chromium trioxide with pyridine and HCl.

bonds occur in oxidation reactions. These are also known as dehydrogenation

ve loss of dihydrogen from an alcohol molecule.

: KMnO4

: CrO3 in anhydrous medium, pyridinium chlorochromate (PCC), a

complex of chromium trioxide with pyridine and HCl.

bonds occur in oxidation reactions. These are also known as dehydrogenation

ve loss of dihydrogen from an alcohol molecule.

: CrO3 in anhydrous medium, pyridinium chlorochromate (PCC), a

(c) Reactions of phenols

1. Electrophilic aromatic substitution:

(i) Nitration: With dilute nitric acid at low temperature (298 K), phenol yields a mixture of

ortho and para nitrophenols.

The ortho and para isomers can be separated by steam distillation.

o-Nitrophenol is steam volatile du

p-nitrophenol is less volatile due to intermolecular hydrogen bonding which causes the

association of molecules.

Formation of Picric acid (2,4,6-

(i)

Phenol phenol-2,4-disulphonic acid

ilic aromatic substitution:

With dilute nitric acid at low temperature (298 K), phenol yields a mixture of

The ortho and para isomers can be separated by steam distillation.

Nitrophenol is steam volatile due to intramolecular hydrogen bonding.

nitrophenol is less volatile due to intermolecular hydrogen bonding which causes the

-trinitrophenol) from phenol:

sulphonic acid Picric acid

With dilute nitric acid at low temperature (298 K), phenol yields a mixture of

e to intramolecular hydrogen bonding.

nitrophenol is less volatile due to intermolecular hydrogen bonding which causes the

Picric acid

(ii)

Phenol

(ii) Halogenation:

(a) When the reaction is carried out in solvents of low polarity such as CHCl3 or CS2

and at low temperature, monobromophenols are formed.

In non-aqueous medium

(b) When phenol is treated

white precipitate.

In aqueous medium

2. Kolbe’s reaction:

Phenoxide ion generated by treating phenol with sodium hydroxide is even more reactive

than phenol towards electrophilic aromatic substituti

substitution with carbon dioxide, a weak electrophile. Ortho hydroxybenzoic acid is

formed as the main reaction product.

Picric acid

When the reaction is carried out in solvents of low polarity such as CHCl3 or CS2

and at low temperature, monobromophenols are formed.

with bromine water, 2,4,6-tribromophenol is formed as

Phenoxide ion generated by treating phenol with sodium hydroxide is even more reactive

than phenol towards electrophilic aromatic substitution. Hence, it undergoes electrophilic

substitution with carbon dioxide, a weak electrophile. Ortho hydroxybenzoic acid is

formed as the main reaction product.

When the reaction is carried out in solvents of low polarity such as CHCl3 or CS2

tribromophenol is formed as

Phenoxide ion generated by treating phenol with sodium hydroxide is even more reactive

on. Hence, it undergoes electrophilic

substitution with carbon dioxide, a weak electrophile. Ortho hydroxybenzoic acid is

3. Reimer-Tiemann reaction:

On treating phenol with chloroform in the presence of sodium hydro

introduced at ortho position of benzene ring. This reaction is known as Reimer

reaction. The intermediate substituted benzal chloride is hydrolysed in the presence of

alkali to produce salicylaldehyde.

4. Reaction of phenol with zinc dust:

Phenol is converted to benzene on heating with zinc dust.

5.Oxidation:

Oxidation of phenol with chromic acid produces a conjugated diketone known as

benzoquinone.

On treating phenol with chloroform in the presence of sodium hydro

introduced at ortho position of benzene ring. This reaction is known as Reimer

reaction. The intermediate substituted benzal chloride is hydrolysed in the presence of

alkali to produce salicylaldehyde.

l with zinc dust:

Phenol is converted to benzene on heating with zinc dust.

Oxidation of phenol with chromic acid produces a conjugated diketone known as

On treating phenol with chloroform in the presence of sodium hydroxide, a –CHO group is

introduced at ortho position of benzene ring. This reaction is known as Reimer - Tiemann

reaction. The intermediate substituted benzal chloride is hydrolysed in the presence of

Oxidation of phenol with chromic acid produces a conjugated diketone known as

In the presence of air, phenols are slowly oxidised to dark coloured mixtures containing

quinones.

(i) By dehydration of alcohols:

Ethanol is dehydrated to ethene in the presence of sulphuric acid at 443 K. At 413 K,

ethoxyethane is the main product.

2. Williamson synthesis:

It is an important laboratory method for the preparation of symmetrical and

unsymmetrical ethers. In this method, an alkyl halide is allowed to react with sodium

alkoxide.

(i)

In the presence of air, phenols are slowly oxidised to dark coloured mixtures containing

Preparation of Ethers

Ethanol is dehydrated to ethene in the presence of sulphuric acid at 443 K. At 413 K,

xyethane is the main product.

It is an important laboratory method for the preparation of symmetrical and

unsymmetrical ethers. In this method, an alkyl halide is allowed to react with sodium

In the presence of air, phenols are slowly oxidised to dark coloured mixtures containing

Ethanol is dehydrated to ethene in the presence of sulphuric acid at 443 K. At 413 K,

It is an important laboratory method for the preparation of symmetrical and

unsymmetrical ethers. In this method, an alkyl halide is allowed to react with sodium

(ii)

Ethers containing substituted alkyl groups (secondary or tertiary) may also be prepared by

this method. The reaction involves SN2 attack of an alkoxide ion on primary alkyl halide.

Phenols are also converted to ethers by this method.

ining substituted alkyl groups (secondary or tertiary) may also be prepared by

this method. The reaction involves SN2 attack of an alkoxide ion on primary alkyl halide.

Phenols are also converted to ethers by this method.

ining substituted alkyl groups (secondary or tertiary) may also be prepared by

this method. The reaction involves SN2 attack of an alkoxide ion on primary alkyl halide.

Physical properties of Ethers:

Boiling point:

Boiling points of Ethers are lower than alcohols. The large difference in boiling points of

alcohols and ethers is due to the presence of hydrogen bonding in alcohols.

Solubility:

The miscibility of ethers with water resembles those of a

mass. This is due to the fact that just like alcohols, oxygen of ether can also form

hydrogen bonds with water molecule

Chemical properties of Ethers:

1.Cleavage of C–O bond in ethers

The reaction of dialkyl ether gives t

Ethers with two different alkyl groups are also cleaved in the same manner.

Boiling points of Ethers are lower than alcohols. The large difference in boiling points of

alcohols and ethers is due to the presence of hydrogen bonding in alcohols.

The miscibility of ethers with water resembles those of alcohols of the same molecular

mass. This is due to the fact that just like alcohols, oxygen of ether can also form

hydrogen bonds with water molecule.

Chemical properties of Ethers:

O bond in ethers:

The reaction of dialkyl ether gives two alkyl halide molecules.

Ethers with two different alkyl groups are also cleaved in the same manner.

Boiling points of Ethers are lower than alcohols. The large difference in boiling points of

alcohols and ethers is due to the presence of hydrogen bonding in alcohols.

lcohols of the same molecular

mass. This is due to the fact that just like alcohols, oxygen of ether can also form

Ethers with two different alkyl groups are also cleaved in the same manner.

Alkyl aryl ethers are cleaved at the alkyl

bond. The reaction yields phenol and alkyl halide.

When one of the alkyl group is a tertiary group, the halide formed is a tertiary halide.

It is because in step 2 of the reaction, the departure of leaving group (HO

more stable carbocation [(CH3)3C

Alkyl aryl ethers are cleaved at the alkyl-oxygen bond due to the more stable aryl

bond. The reaction yields phenol and alkyl halide.

ne of the alkyl group is a tertiary group, the halide formed is a tertiary halide.

It is because in step 2 of the reaction, the departure of leaving group (HO

more stable carbocation [(CH3)3C+], and the reaction follows SN1 mechanism

oxygen bond due to the more stable aryl-oxygen

ne of the alkyl group is a tertiary group, the halide formed is a tertiary halide.

It is because in step 2 of the reaction, the departure of leaving group (HO–CH3) creates a

], and the reaction follows SN1 mechanism

2. Electrophilic substitution:

the alkoxy group (-OR) is ortho, para directing and activates the aromatic ring towards

electrophilic substitution.

(i) Halogenation:

(ii) Friedel-Crafts reaction:

(iii) Nitration:

Anisole reacts with a mixture of conc

of ortho and para nitro anisole.

OR) is ortho, para directing and activates the aromatic ring towards

Anisole reacts with a mixture of concentrated sulphuric and nitric acids to yield a mixture

of ortho and para nitro anisole.

OR) is ortho, para directing and activates the aromatic ring towards

entrated sulphuric and nitric acids to yield a mixture

NCERT TEXTBOOK QUESTIONS

Page No.317

Answer:11.1

Primary alcohols: (i), (ii), (iii) Secondary alcohols: (iv), (v) Tertiary alcohols: (vi)

Answer: 11.2

(ii) and (iv) i.e. H2C=CH – CH

Page No.320

Answer: 11.3

NCERT TEXTBOOK QUESTIONS

CH2OH and

Page No.325

Answer: 11.4

Answer:11.5

Page No. 335

Answer: 11.6

Answer:11.7

Answer: 11.8

The resonance structures of o-and p- nitro phenoxide ions and phenoxide ion are given

below:

Answer:11.9

(i) Reimer-Tiemann reaction

Page No.342

Answer:11.10

In Williamsons’ synthesis, the alkyl halide should be primary. Thus, the alkyl halide should

be derived from ethanol and the alkoxide ion from 3-methylpentan-2-ol. The synthesis is

as follows

Answer:11.11

Page No. 343

Answer:11.12

NCERT EXERCISES

Page No.344

Answer:11.1

(i) 2,2,4-Trimethylpentan-3-ol

(ii) 5-Ethylheptane-2,4-dioI

(iii) Butane-2,3-diol

(iv)Propane-1,2,3-triol

(v)2-Methylphenol

(vi)4-Methylphenol

(vii) 2,5-DimethylphenoI

(viii) 2,6-Dimethylphenol

(ix)1-Methoxy-2-methylpropane

(x)Ethoxy benzene

(xi)1-Phenoxyheptane

(xii) 2-Ethoxybutane

Answer: 11.2

methylpropane

Answer:11.3

Eight isomers are possible. These are:

Answer:11.4

The molecules of butane are held together by weak van der Waal’s forces of attraction

while those of propanol are held together by stronger intermolecular hydrogen bonding.

Answer:11.5

Alcohols can form hydrogen bonds with water and by breaking the hydrogen bonds

already existing between water molecules. Therefore, they are soluble in water.

On the other hand, hydrocarbons cannot from hydrogen bonds with water and hence are

insoluble in water.

Answer: 11.6

The addition of diborane to alkenes to form trialkyl boranes followed by their oxidation

with alkaline hydrogen peroxide to form alcohols is called hydroboration-oxidation. For

example,

Answer:11.7

The three isomers are:

Answer:11.8

Intramolecular H – bonding is present in o

steam volatile.

In p – nitrophenol, the molecules are strongly associated due to the existence of

intermolecular bonding.

Answer 11.9

From cumene

From cumene Phenol is manufactured from the hydrocarbon, cumene. Cumene (isopropyl

benzene) is oxidised in the presence of air to cumene

phenol and acetone by treating it with dilute acid. Acetone, a by

is also obtained in large quantities by this method.

bonding is present in o – nitrophenol therefore, o

enol, the molecules are strongly associated due to the existence of

From cumene Phenol is manufactured from the hydrocarbon, cumene. Cumene (isopropyl

benzene) is oxidised in the presence of air to cumene hydroperoxide. It is converted to

phenol and acetone by treating it with dilute acid. Acetone, a by-product of this reaction,

is also obtained in large quantities by this method.

therefore, o – nitrophenol is

enol, the molecules are strongly associated due to the existence of

From cumene Phenol is manufactured from the hydrocarbon, cumene. Cumene (isopropyl

hydroperoxide. It is converted to

product of this reaction,

Answer:11.10

Chlorobenzene is fused with NaOH at 623K and 320 atmospheric

obtained by acidification of sodium phenoxide so produced.

Answer:11.11

There are three steps which are involved in the mechanism of hydration of ethene to

form ethanol. these steps are as follows:

Step 1:

Protonation of ethene to form carbocation by an electrophilic attack of H

Step 2:

Nucleophilic attack of water on carbocation:

Step 3:

Deprotonation to form ethanol:

Chlorobenzene is fused with NaOH at 623K and 320 atmospheric pressure. Phenol is

obtained by acidification of sodium phenoxide so produced.

There are three steps which are involved in the mechanism of hydration of ethene to

form ethanol. these steps are as follows:

rm carbocation by an electrophilic attack of H

Nucleophilic attack of water on carbocation:

Deprotonation to form ethanol:

pressure. Phenol is

There are three steps which are involved in the mechanism of hydration of ethene to

rm carbocation by an electrophilic attack of H3 O +:

Answer:11.12

Answer:11.13

By acid-catalysed hydration of ethylbenzene ( styrene ), 1

synthesized.

(i) When chloromethyl cyclohexane is treated with sodium hydroxide, cyclohexyl

methanol is obtained.

(ii) When 1 – chloropentane is treated with NaOH, pentan

Answer:11.14

The acidic nature of phenol can be proven with

(i) Phenol reacts with sodium to give sodium phenoxide, liberating H

catalysed hydration of ethylbenzene ( styrene ), 1 – phenyl ethanol ca

When chloromethyl cyclohexane is treated with sodium hydroxide, cyclohexyl

methanol is obtained.

chloropentane is treated with NaOH, pentan – 1 –

The acidic nature of phenol can be proven with the two reactions given below:

(i) Phenol reacts with sodium to give sodium phenoxide, liberating H2

phenyl ethanol can be

When chloromethyl cyclohexane is treated with sodium hydroxide, cyclohexyl

– ol is produced.

the two reactions given below:

2.

(ii)Phenol reacts with sodium hydroxide to give sodium phenoxide & water as by

products.

The acidity of phenol is more than that of ethanol. This is

the phenoxide ion undergoes resonance & gets stabilized whereas ethoxide ion does not.

Answer:11.15

Ortho nitrophenol is more acidic than ortho methoxyphenol

The nitro-group is an electron-withdrawing group. The presence

position decreases the electron density in the O

proton. Also, the o-nitro phenoxide ion formed after the loss of protons is stabilized by

resonance. Hence, ortho nitrophenol is a stron

On the other hand, methoxy group is an electron

electron density in the O-H bond and hence, the proton cannot be given out easily.

Answer:11.16

The density of the electron increases in the benzene ring as t

electron-donating group. This is clearly shown in the resonance structure of phenol given

here

(ii)Phenol reacts with sodium hydroxide to give sodium phenoxide & water as by

The acidity of phenol is more than that of ethanol. This is because after losing a proton,

the phenoxide ion undergoes resonance & gets stabilized whereas ethoxide ion does not.

Ortho nitrophenol is more acidic than ortho methoxyphenol

withdrawing group. The presence of this group in the ortho

position decreases the electron density in the O-H bond. As a result, it is easier to lose a

nitro phenoxide ion formed after the loss of protons is stabilized by

resonance. Hence, ortho nitrophenol is a stronger acid.

On the other hand, methoxy group is an electron-releasing group. Thus, it increases the

H bond and hence, the proton cannot be given out easily.

The density of the electron increases in the benzene ring as the – OH group acts as an

donating group. This is clearly shown in the resonance structure of phenol given

(ii)Phenol reacts with sodium hydroxide to give sodium phenoxide & water as by-

because after losing a proton,

the phenoxide ion undergoes resonance & gets stabilized whereas ethoxide ion does not.

of this group in the ortho

H bond. As a result, it is easier to lose a

nitro phenoxide ion formed after the loss of protons is stabilized by

releasing group. Thus, it increases the

H bond and hence, the proton cannot be given out easily.

OH group acts as an

donating group. This is clearly shown in the resonance structure of phenol given

As a result, the benzene ring is activated towards electrophilic substitution.

Answer:11.17

(i)

(ii)

(iii)

(iv)

As a result, the benzene ring is activated towards electrophilic substitution.

As a result, the benzene ring is activated towards electrophilic substitution.

Answer:11.18

(i) Kolbe’s reaction:

Sodium phenoxide is formed when phenol is treated with sodium hydroxide. Ortho

hydroxybenzoic acid as the main product when sodium phenoxide is treated with carbon

dioxide, followed by acidification, it undergoes electrophilic subst

known as Kolbe’s reaction.

(ii) Reimer – Tiemann reaction:

A -CHO group is introduced at the ortho position of the benzene ring when phenol is

treated with chloroform (CHCl3

This reaction is known as the Reimer

Salicylaldehyde is produced when the intermediate is hydrolyzed in the presence of

alkalis.

(iii) Williamson ether synthesis:

A chemical method to synthesize symmetrical & unsymmetrical ethers by making alkyl

halides to react with sodium alkoxides is called Williamson ether synthesis.

Sodium phenoxide is formed when phenol is treated with sodium hydroxide. Ortho

hydroxybenzoic acid as the main product when sodium phenoxide is treated with carbon

dioxide, followed by acidification, it undergoes electrophilic substitution. This reaction is

Tiemann reaction:

CHO group is introduced at the ortho position of the benzene ring when phenol is

3) in the presence of sodium hydroxide.

is known as the Reimer – Tiemann reaction.

is produced when the intermediate is hydrolyzed in the presence of

Williamson ether synthesis:

A chemical method to synthesize symmetrical & unsymmetrical ethers by making alkyl

lides to react with sodium alkoxides is called Williamson ether synthesis.

Sodium phenoxide is formed when phenol is treated with sodium hydroxide. Ortho –

hydroxybenzoic acid as the main product when sodium phenoxide is treated with carbon

itution. This reaction is

CHO group is introduced at the ortho position of the benzene ring when phenol is

) in the presence of sodium hydroxide.

is produced when the intermediate is hydrolyzed in the presence of

A chemical method to synthesize symmetrical & unsymmetrical ethers by making alkyl

lides to react with sodium alkoxides is called Williamson ether synthesis.

The above reaction includes Sn

of primary alkyl halides, better results are obtained.

Only If the alkyl halide is tertiary or secondary, in that case, elimination competes over

substitution.

(iv) Unsymmetrical ether:

When an oxygen atom has two groups on two of its side, it is called

(i.e., the number of carbon atoms is unequal). For e

CH2 CH3).

Answer11.19:

The mechanism of acid dehydration of ethanol to yield ethene involves the following

three steps:

Step 1:

Formation of ethyl oxonium by protonation of ethanol:

Step 2:

A carbocation is formed (rate-determini

Step 3:

Ethane is formed by elimination of proton:

The above reaction includes Sn 2 attack of the alkoxide ion on the alkyl halide. In the case

of primary alkyl halides, better results are obtained.

ertiary or secondary, in that case, elimination competes over

When an oxygen atom has two groups on two of its side, it is called Unsymmetrical ether.

(i.e., the number of carbon atoms is unequal). For e.g.: ethyl methyl ether (CH

The mechanism of acid dehydration of ethanol to yield ethene involves the following

Formation of ethyl oxonium by protonation of ethanol:

determining step):

Ethane is formed by elimination of proton:

attack of the alkoxide ion on the alkyl halide. In the case

ertiary or secondary, in that case, elimination competes over

Unsymmetrical ether.

methyl ether (CH3 – O −

The mechanism of acid dehydration of ethanol to yield ethene involves the following

The acid is released in Step 3 which was being consumed in

the equilibrium in a forward direction, after ethene is formed.

Answer:11.20

(i) when propene is reacted with water in the presence of an acid as a catalyst, as a result,

we obtain propan – 2 – ol.

(ii) If then benzyl alcohol is obtained when benzyl chloride is reacted with NaOH which is

then followed by acidification.

(iii) An adduct is the obtained when ethyl magnesium chloride is reacted with methanal,

as a result, propan – 1 – ol on hydrolysis is obtained.

(iv) On treating methyl magnesium bromide with propane, an adduct is obtained which

results in 2 – methylpropane –

which was being consumed in Step 1. It is removed to shift

the equilibrium in a forward direction, after ethene is formed.

cted with water in the presence of an acid as a catalyst, as a result,

(ii) If then benzyl alcohol is obtained when benzyl chloride is reacted with NaOH which is

when ethyl magnesium chloride is reacted with methanal,

ol on hydrolysis is obtained.

(iv) On treating methyl magnesium bromide with propane, an adduct is obtained which

2 – ol on hydrolysis.

Step 1. It is removed to shift

cted with water in the presence of an acid as a catalyst, as a result,

(ii) If then benzyl alcohol is obtained when benzyl chloride is reacted with NaOH which is

when ethyl magnesium chloride is reacted with methanal,

(iv) On treating methyl magnesium bromide with propane, an adduct is obtained which

Answer 11.21:

(i) NaBH4 or LiAlH4

(ii) 85 % phosphoric acid

(iii) Acidified potassium permanganate

(iv) Bromine water

(v) Pyridinium chlorochromate (PCC)

(vi) Acidified potassium permanganate

Answer 11.22:

Ethanol experiences intermolecular H

which results in the association of molecules. additional energy is necessary to break

these hydrogen bonds. Conversely, methoxymethane does not experience H

Therefore, ethanol has a higher boiling point when c

Answer 11.23:

(i) 1 – Ethoxy – 2 – methylpropane

(ii) 2 – Chloro – 1 – methoxy ethane

(iii) 4 – Nitro anisole

(iv) 1 – Methoxy propane

(v) 1 – Ethoxy – 4, 4 – dimethyl cyclohexane

(vi) Ethoxy benzene

(iii) Acidified potassium permanganate

(v) Pyridinium chlorochromate (PCC)

(vi) Acidified potassium permanganate

Ethanol experiences intermolecular H – bonding because of the presence of

which results in the association of molecules. additional energy is necessary to break

these hydrogen bonds. Conversely, methoxymethane does not experience H

Therefore, ethanol has a higher boiling point when compared to methoxymethane

methylpropane

methoxy ethane

dimethyl cyclohexane

use of the presence of – OH group,

which results in the association of molecules. additional energy is necessary to break

these hydrogen bonds. Conversely, methoxymethane does not experience H – bonding.

ompared to methoxymethane

Answer 11.24:

(i)

(ii)

(iii)

(iv)

Answer11.25:

The reaction of Williamson synthesis includes SN

alkyl halide.

while, tertiary alkyl halides or secondary alkyl halides were to be substituted in place of

primary alkyl halides, in that case elimination would contend over substitution. This

results in the formation of alkenes. This happens because alkoxides are nucleophiles as

well as strong bases. Therefore, they react with alkyl halides, which results in an

elimination reaction.

The reaction of Williamson synthesis includes SN 2 attack of an alkoxide ion on a primary

while, tertiary alkyl halides or secondary alkyl halides were to be substituted in place of

in that case elimination would contend over substitution. This

results in the formation of alkenes. This happens because alkoxides are nucleophiles as

well as strong bases. Therefore, they react with alkyl halides, which results in an

attack of an alkoxide ion on a primary

while, tertiary alkyl halides or secondary alkyl halides were to be substituted in place of

in that case elimination would contend over substitution. This

results in the formation of alkenes. This happens because alkoxides are nucleophiles as

well as strong bases. Therefore, they react with alkyl halides, which results in an

Answer 11.26:

1 – propoxypropane can be synthesized from propan

Propan – 1 – ol undergoes dehydration in the presence of protic acids (such as H

H3PO4) to give 1 – propoxypropane.

The mechanism of this reaction involves

Step 1: Protonation

Step 2: Nucleophilic attack

Step 3: Deprotonation

Answer 11.27:

The synthesis of ethers with dehydration of alcohol is a bimolecular reaction ( SN

involves the attack of an alcohol molecule on

method, the alkyl group should be unhindered. In the case of secondary or tertiary

alcohols, the alkyl group is hindered. As a result, elimination of dominates substitution.

Hence, in place of ethers, alkenes are forme

Answer 11.28:

(i)

propoxypropane can be synthesized from propan – 1 – ol by dehydration.

ol undergoes dehydration in the presence of protic acids (such as H

propoxypropane.

The mechanism of this reaction involves the following three steps:

The synthesis of ethers with dehydration of alcohol is a bimolecular reaction ( SN

involves the attack of an alcohol molecule on a protonated alcohol molecule. In the

method, the alkyl group should be unhindered. In the case of secondary or tertiary

alcohols, the alkyl group is hindered. As a result, elimination of dominates substitution.

Hence, in place of ethers, alkenes are formed.

ol by dehydration.

ol undergoes dehydration in the presence of protic acids (such as H2SO4,

The synthesis of ethers with dehydration of alcohol is a bimolecular reaction ( SN2 ) which

a protonated alcohol molecule. In the

method, the alkyl group should be unhindered. In the case of secondary or tertiary

alcohols, the alkyl group is hindered. As a result, elimination of dominates substitution.

(ii)

(iii)

Answer 11.29:

(i)

The electron density in the benzene ring boosts up because of the existence of + R effect

of the alkoxy group In aryl alkyl ethers which is given in the resonance configuration

below:

Therefore, a benzene ring is activated by the alkoxy group towards electrophilic

substitution.

(ii) The above resonance configuration, we infer that the electron density is higher at the

para & ortho positions compared to meta position. consequently, the substituen

incoming is directed to the para & ortho positions in the benzene ring.

Answer 11.30:

The steps of the reaction of methoxymethane with HI are given below :

Step 1 : Protonation of methoxymethane :

The electron density in the benzene ring boosts up because of the existence of + R effect

of the alkoxy group In aryl alkyl ethers which is given in the resonance configuration

benzene ring is activated by the alkoxy group towards electrophilic

The above resonance configuration, we infer that the electron density is higher at the

para & ortho positions compared to meta position. consequently, the substituen

incoming is directed to the para & ortho positions in the benzene ring.

The steps of the reaction of methoxymethane with HI are given below :

Protonation of methoxymethane :

The electron density in the benzene ring boosts up because of the existence of + R effect

of the alkoxy group In aryl alkyl ethers which is given in the resonance configuration

benzene ring is activated by the alkoxy group towards electrophilic

The above resonance configuration, we infer that the electron density is higher at the

para & ortho positions compared to meta position. consequently, the substituent which is

incoming is directed to the para & ortho positions in the benzene ring.

The steps of the reaction of methoxymethane with HI are given below :

Step 2: Nucleophilic attack of I

Step 3: The methanol synthesized in the above step is made to react with another HI

molecule which then converts to methyl iodide. This is done at a high temperature & HI is

present in excess.

Answer 11.31:

(i)

(ii)

– :

The methanol synthesized in the above step is made to react with another HI

molecule which then converts to methyl iodide. This is done at a high temperature & HI is

The methanol synthesized in the above step is made to react with another HI

molecule which then converts to methyl iodide. This is done at a high temperature & HI is

(iii)

(iv)

Answer11.32:

The alcohols given above can be synthesized by applying Markovnikov’s rule of acid

catalysed hydration of appropriate alkenes.

given above can be synthesized by applying Markovnikov’s rule of acid

hydration of appropriate alkenes.

given above can be synthesized by applying Markovnikov’s rule of acid-

Acid-catalysed hydration of pent

pentan3-ol.

Thus, the first reaction is preferred over the second one to get pentan

(iv)

Answer 11.33:

The steps of the reaction given above involve the following procedure :

Step 1: Protonation

Step 2: Forming 2 ° carbonation by eliminating the water molec

Step 3: Re – arranging by the shifting hydride

Step 4: Nucleophilic attack

hydration of pent-2-ene also produces pentan-2-ol but along with

Thus, the first reaction is preferred over the second one to get pentan

The steps of the reaction given above involve the following procedure :

Forming 2 ° carbonation by eliminating the water molecule

arranging by the shifting hydride – ion

ol but along with

Thus, the first reaction is preferred over the second one to get pentan-2-ol.

The steps of the reaction given above involve the following procedure :