3. These classes of compounds find wide applications in industry as well as in
day-to-day life.
●
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.
4. Alcohol Phenol Ether
●
Functional group
hydroxyl (-OH )
●
–OH group is bonded
to an alkyl group.
●
Formula R-OH.
●
Functional group
hydroxyl (-OH )
●
–OH group is bonded
to an aryl group
●
Formula Ar-OH.
●
Functional group
–O – group (oxy group).
●
Oxy group is bonded
to Ar or R
●
Formula Ar-O/R-O
These are compounds containing C – O single bond.
Hydroxy derivative of
aliphatic hydrocarbons
Hydroxy derivatives of
arenes
Dialkyl or diaryl
derivatives of Water
7. Allylic alcohols:
—OH group is attached to
a sp3 hybridised carbon adjacent to
the carbon-carbon double
bond
2 Benzylic alcohols:
—OH group is attached
to a sp3
—hybridised carbon atom next to
an aromatic ring
3
8. (ii) Compounds containing C sp 2
− OH bond:
—OH group bonded to a carbon-carbon double bond,
Vinylic alcohol: CH 2
= CH – OH
11.1.2 Phenols— Mono, Di and trihydric phenols
9. ●
11.1.3 Ethers
Simple or symmetrical Mixed or unsymmetrical
Alkyl or aryl groups attached to
the oxygen atom are the same
Alkyl or aryl groups attached to
the oxygen atom are different
C 2
H 5
O C 2
H 5
,
C 2
H 5
O CH 3
C 2
H 5
O C 6
H 5
13. 11.3 Structures of Functional Groups
Oxygen of the –OH group is attached to carbon by a sigma ( σ ) bond
Formed by
the overlap of
a sp3
hybridised orbital of C
with a sp3
hybridised orbital of O
In alcohols,
Due to the repulsion between the unshared electron pairs of oxygen
Bond angle is slightly <
the tetrahedral angle (109°-28′).
14. –OH group is attached to sp 2
hybridised carbon of an aromatic ring.
Carbon– oxygen bond length (136 pm) in phenol
is slightly less than that in methanol.
This is due to
(i) partial double bond character on account of the conjugation
of unshared electron pair of oxygen with the aromatic ring
(ii) sp2
hybridised state of carbon to which oxygen is
attached.
In phenols
15. In ethers
The four electron pairs, i.e., are arranged approximately
in a tetrahedral arrangement.
Two lone pairs of electrons on oxygen
➔
The bond angle is slightly greater than the tetrahedral angle due to the
repulsive interaction between the two bulky (–R) groups.
➔
The C–O bond length (141 pm) is almost the same as in alcohols.
Two bond pairs +
16. 11.4 Alcohols and Phenols
11.4.1 Preparation of Alcohols
1. From alkenes
(i) By acid catalysed hydration:
acid as catalyst
water
Markovnikov’s rule
H +
OH-
Alcohol
20. Addition of water to the alkene in a way opposite to the Markovnikov’s rule.
+ B2
H6
H2
O2
BH3
21. 2. From carbonyl compounds
(i) By reduction of aldehydes and ketones
Aldehydes ---------> Primary alcohols
Ketones ------------> Secondary alcohols.
Addition of hydrogen in the presence of catalysts (catalytic hydrogenation)
/Pt / Ni
/Lithium aluminium hydride (LiAlH 4 ).
Primary alcohols
Secondary alcohols.
Focus
Area
22. ii) By reduction of carboxylic acids and esters:
(catalytic hydrogenation).
LiAlH 4
is an expensive reagent,
Used for preparing special chemicals
Commercially
Alcohol
Alcohol
23. 3. From Grignard reagents
Nucleophilic addition of Grignard reagent to the carbonyl group
Alcohol
Focus
Area
29. 11.4.3 Physical Properties
Alcohols and phenols consist of two parts,
Akyl/aryl group Hydroxyl group.
Properties of alcohols and phenols
are chiefly due
to the hydroxyl group.
Boiling Points
●
The boiling points of alcohols and phenols ↑ with↑ in the number of carbon atoms
(increase in van der Waals forces).
●
In alcohols,BP ↓ with ↑of branching in carbon chain
(because of↓ in van der Waals forces with ↓ in surface area).
31. Solubility
Due to their ability to form hydrogen
bonds with water molecules
The solubility decreases with increase in size
of alkyl/aryl (hydro-phobic) groups.
of alcohols and phenols in water
32. 11.4.4 Chemical Reactions
Nucleophiles : The bond between O–H is broken
Electrophiles : The bond between C–O is broken
Alcohols are versatile compounds.
They react both as
33. (a) Reactions involving cleavage of
O–H bond
1. Acidity of alcohols and phenols
(i) Reaction with metals:
2. Esterification
(b) Reactions involving cleavage of
carbon – oxygen (C–O) bond in
alcohols
1. Reaction with hydrogen halides:
2. Reaction with phosphorus trihalides:
3. Dehydration:
4. Oxidation:
34. ii) Acidity of alcohols:
●
Alcohols behave as Weak acids & ionise to very small extent
●
Acidic character of alcohols is due to the polarity of O-H bond
●
O atom more EN pulls the shared pair of electrons of O-H bond
●
The shared pair shifts towards O atom & the O-H bond becomes weak.
●
This facilitates the release of a proton (H+) from the molecules
35. Alcohols are, weaker acids than water.
●
In Water -OH Group is attached to a H atom
●
In Alcohols -OH group is linked to an alkyl group
Due low polarity of O-H bond the release of H+ ions in Alcohols become more
difficult as compared to that in water,
●
alcohols ionise to a lesser extent & shows lesser acidic strength than water
H-OH
R---OH
Electron releasing groups
and increase the electron density
at the O-atom due to +I effect
This decrease the polarity
of O-H bond
In alcohols the oxygen atom shows lesser tendency
to attract the shared electrons of O-H bond,
O-H bond in alcohols
is less polar than in water
36. Alcohols are, weaker acids than water.
Water is a better proton donor
(i.e., stronger acid) than alcohol.
Alkoxide ion is a better proton acceptor
than hydroxide ion,
alkoxides are stronger bases
R-O-Na is a stronger base than NaOH.
37. ii) Acidity of alcohols: Acid strength of alcohols ↓
Presence of one or more alkyl groups ↓ the polarity of O-H bond & ↓ the acidic strength
O
Electron releasing groups
and increase the electron density
at the O-atom due to +I effect
This decrease the polarity
of O-H bond
38. (i) Reaction with metals:
Another method
The above reactions show that
Alcohols and phenols are acidic in nature
39. (i) Reaction with metals:
Alcohols and phenols are Brönsted acids
i.e., they can donate a proton to a stronger base (B:).
Alcohols act as Bronsted bases as well.
Due to the presence of unshared electron pairs on oxygen
Which makes them proton acceptors.
40. (iii) Acidity of phenols:
Due to this, the charge distribution in phenol molecule, as depicted in its resonance
structures,causes the oxygen of –OH group to be positive.
Eg: Reaction with Na,Al & NaOH
sp2
hybridised carbon
Hydroxyl group, ---->Electron withdrawing group. Phenols are acidic in nature.
41. (iii) Acidity of phenols:
Phenols are more acidic than alcohols
is explained in terms of the greater stability of phenoxide ion
due to resonance stabilisation
Oxygen atom of the OH group acquires a partial charge,
Due to the presence of positive charge ,
the oxygen atom pulls the shared pair of O-H bond
This facilitates the release of proton
42. The reaction of phenol with aqueous sodium hydroxide
indicates that phenols are stronger acids than alcohols and water.
Hydroxyl group attached to an aromatic ring
is more acidic than the one in which
hydroxyl group is attached to an alkyl group.
43. Due to the higher electronegativity of sp2
hybridised carbon of phenol to which –OH is
attached, electron density decreases on oxygen.
This increases the polarity of O–H bond &
increase in ionisation of phenols than that of alcohols.
44. There is also charge delocalisation in phenol, its resonance structures have charge
separation due to which the phenol molecule is less stable than phenoxide ion.
.
.
In alkoxide ion, the negative charge is localised on oxygen
In phenoxide ion, the charge is delocalised.
Phenoxide ion more stable and favours the ionisation of phenol.
45. In substituted phenols
These groups withdraw electrons from the ring disperse the negative charge &
increase the stability of the phenoxide ion .
This increase the acidic strength
The presence of electron withdrawing
groups such as nitro , halogen group,
enhances the acidic strength of Phenol .
46. This effect is more pronounced when such a group is present at ortho and para positions.
-NO2
group present at the o & p can exert both -I effect & -R effect & can enter into
resonance with the -OH group
NO2
group present at the m position cannot enter into resonance
ortho and para phenols are more acidic
There is effective delocalisation of negative charge in phenoxide ion when
substituent is at ortho or para position.
47. Alkyl groups exert +R effect such groups donate electrons into the
ring system & phenoxide ion get negative charge,
This decrease acidic strength of phenol
Cresols, for example, are less acidic than phenol.
On the other hand,electron releasing groups
48. 2. Esterification
Ester
Carboxylic acids
Ester
Acid anhydride
Acid chlorides Ester
Acid
Acid
Base
Reaction is reversible, water is removed as
soon as it is formed.
to neutralise HCl
Shifts the equilibrium to the right hand side
49. . The introduction of acetyl (CH 3
CO) group in alcohols or phenols .
Acetylation:
Acetylation of salicylic acid produces aspirin.
50. 1. Reaction with hydrogen halides:
2. Reaction with phosphorus trihalides
3. Dehydration
4. Oxidation:
(b) Reactions involving
cleavage of (C–O)
bond
in alcohols
52. Lucas
Reagent
Alcohols
Insoluble in water and
produce turbidity in solution.
Alkyl
Halides
+
Lucas Test----->
Distinction between Primary, Secondary and Tertiary alcohols.
= Concentrated hydrochloric Acid + Anhydrous Zinc chloride
= Conc.HCl + Anhy.ZnCl2
Lucas Reagent
Focus
Area
54. 2. Reaction with Phosphorus trihalides
Alcohol Phosphorus trihalides
55. 3. Dehydration (Removal of a molecule of water)
Concentrated H 2
SO 4
or H 3
PO 4
Catalysts ----> Anhydrous zinc chloride or alumina
Tertiary
Secondary
Primary
Alkene
Alkene
Alkene
Focus
Area
56. Relative ease of dehydration of alcohols follows the following order:
Tertiary carbocations are more stable and therefore are easier to form tertiary
alcohols are the easiest to dehydrate.
than secondary and primary carbocations;
57. Acid used
Acid is released
To drive the equilibrium to the right, ethene is removed as it is formed
58. 4. Oxidation:
Depending on the oxidising agent used,
Cleavage of an C-H and O-H bonds + Formation of a carbon- oxygen double bond
(Carbonyl)
Dehydrogenation(loss of dihydrogen)
Oxidation
10
alcohol
59. Primary alcohol is oxidised to an aldehyde
Secondary alcohols are oxidised to ketones
Tertiary alcohols do not undergo oxidation reaction
Oxidation
ation
62. (c) Reactions of phenols
1. Electrophilic aromatic substitution
The –OH group directs the incoming group to ortho and para
positions in the ring as these positions become electron rich
due to the resonance effect caused by –OH group
The –OH group attached to the benzene ring activates
it towards electrophilic substitution
63. (i) Nitration:
Phenol
Phenol
Strong acid due to the presence
of three electron withdrawing –NO 2
groups which facilitate the
release of hydrogen ion.
Focus
Area
64. The ortho and para isomers can be separated by steam distillation.
Steam volatile Less volatile
.
Association
of molecules
Phenol
68. 4. Reaction of phenol with zinc dust
5. Oxidation
conjugated diketone
Phenol
Phenol
69. 11.5 Some Commercially Important Alcohols
1. Methanol 2. Ethanol
‘Wood spirit’, was produced by destructive
distillation of wood.
catalytic hydrogenation
Fermentation
sugar
Methanol Ethanol
Focus
Area
70. Ethanol
●
Colourless liquid
●
BP 351 K.
●
Used as a solvent in paint industry
●
Preparation of a number of
carbon compounds.
●
Colourless liquid
●
BP 337 K.
●
It is highly poisonous in nature.
●
Used as a solvent in paints,
varnishes
●
For making formaldehyde.
Methanol Focus
Area
71. Denaturation of alcohol.
Commercial alcohol +
Copper sulphate (to give it a colour)
Pyridine (a foul smelling liquid).
&
Made unfit
for drinking
75. The reaction involves S N
2 attack of an alkoxide ion on Primary alkyl halide.
CH3
O
-
Na+
+ CH3
Br--------------------> CH3
-O - CH3
+Na Br
Sodium alkoxide. Alkyl halide Ether
Ether
76. Secondary and tertiary alkyl halides, elimination competes over substitution.
No ether
Alkene
Alkoxides react with alkyl halides leading to elimination reactions.
Alkoxides are not only nucleophiles but strong bases
as well
78. 11.6.2 Physical Properties
The C-O bonds in ethers are polar and thus, ethers have a net dipole
moment.
The large difference in boiling points of alcohols and ethers is
Due to the presence of hydrogen bonding in alcohols.
81. When one of the alkyl group is a tertiary group, the halide formed is a tertiary halide.
Tertiary halide
Reaction follows S N
1 mechanism.
82. 2. Electrophilic substitution
The alkoxy group (-OR) is ortho, para directing and
activates the aromatic ring towards electrophilic substitution in the same way
as in phenol.
