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  1. >>Class 12
  2. >>Chemistry
  3. >>Alcohols, Phenols and Ethers
Deep dive on Tough topics
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Alcohols, Phenols And Ethers

- Finding a topic tough. Let us make it easy for you
1
Trends in physical properties of alcohols
Trends are never easy to remember. But if we understand the reason behind the trends, we can make our work simpler.
Solubility is an important physical property to study in this chapter.
Before we come around to talk about the trend in solubility, we should first look at the structure of alcohol.
You may well remember the structure of a soap molecule. Are you thinking what has soap has to do with alcohols? Well, alcohols have a structure similar to that of a soap molecule. How? Let's see.
Soap has a polar head and non polar tail, the polar head is hydrophilic and the non-polar tail is hydrophobic
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The structure of an alcohol can be described in a similar manner. The oxygen atom in the hydroxy group, makes alcohols polar.
Similar to a soap molecule, the polar part can interact with the water molecules. The lower alcohols have a very short non-polar tail(-R, the alkyl group), and so, they are miscible in water. But as the length of the tail grows, the solubility of alcohol in water decreases.
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Let's look at the next physical property - Boiling point
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If you study the bar diagram above, you will see that alcohols have a higher boiling point than alkanes of comparable molecular masses. This is because the alkanes are held together by weak van der Waals forces. But the molecules of alcohols engage in intermolecular hydrogen bonding, which greatly increases their boiling points.
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Next, when you compare the boiling points of the homologous series, you will see a trend like this:
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The boiling point increases with the increase in the size of the carbon chain. Why does this happen? With the increase in the size of the carbon chain, intermolecular interactions(van der Waals and dipole-dipole) increase. As a result, more energy is required to overcome the intermolecular interaction, which ultimately increases the boiling point
Here are some questions you can attempt from this topic:-
Butane has a _______ boiling point to that of propanol.
A
higher
B
similar
C
lower
D
none of these
Alcohols containing only up to ___________ carbon atoms are completely miscible with water.
A
three
B
four
C
five
D
two
2
Out of the O-H and C-O bonds in alcohol, which will break and under what condition?
Reactions of alcohols are tricky. Some reactions involve the cleavage of the C-O bond, while some reactions involve the cleavage of the O-H bond. Here is a rather simple way to remember this:
Reactions taking place in Basic medium
Alcohols act as acids in basic medium, they can easily lose their H+ ion and form alkoxide ion.
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Most of the reactions that take place in basic medium or with base, involve the breaking of O-H bond.
Reactions taking place in Acidic medium
Alcohols accept hydrogen ion from the acidic medium to form protonated alcohol.
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is a great leaving group, hence, the C-O bond easily breaks in this case.
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There is an exception to this rule:
Esterification reaction - the reaction takes place in an acidic medium, but the OH bond in alcohol breaks.
Want to practice? Try these out
Which one of the following reagents can not cause bond fission in alcohols?
A
B
C
D
Sodium
Which group can be completely displaced by a halogen group?
A
Hydroxyl group(OH)
B
Aldehyde group
C
Nitro group
D
Keto group
Assertion
STATEMENT-1 : An alcohol does not react with ion in aqueous medium, but reacts with concentrated solution to form alkyl chloride.
Reason
STATEMENT-2 : The strong acid accelerates the removal of proton from group of alcohol.
A
STATEMENT-1 is True, STATEMENT-2 is True; STATEMENT-2 is a correct explanation for STATEMENT-1
B
STATEMENT-1 is True, STATEMENT-2 is True; STATEMENT-2 is NOT a correct explanation for STATEMENT-1
C
STATEMENT-1 is True, STATEMENT-2 is False
D
STATEMENT-1 is False, STATEMENT-2 is True
3
Williamson Synthesis
Williamson Synthesis is one of the most important reactions for the preparation of ethers.
It's an reaction between a deprotonated alcohol [alkoxide] and an alkyl halide.
Many questions are asked from this topic. So, keep reading to prepare the topic well.
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Why do we use and not as the nucleophile?
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Which alkyl halide works better in Williamson Ether Synthesis?
Let's take the case of Methyl Halides and other Primary Alkyl halides.
They work well because there is more room for the alkoxide to attack methyl and primary alyl halides.
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When we take an secondary alkyl halide, elimination reaction competes with nucleophilic substitution reaction. This can be minimised by conducting the reaction in an aprotic solvent like DMSO(Dimethyl Sulphoxide)
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In the case of tertiary alkyl halides, there is no room for attack by the nucleophile(alkoxide). therefore elimination reaction takes place instead of substitution.
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So, how do we prepare t-butyl ether by Williamson synthesis reaction?
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To figure out the possible reactants, let's break the bond in two places A and B as in the image below.
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If we consider the Possibility A, the reactants would be:-
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Since a tertiary halide is involved, reaction can not take place to form an ether, instead an alkene is formed by elimination reaction. If we consider the Possibility B, the reactants would be:-
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Since a primary halide is involved here, substitution will take place to give the desired ether, i.e. t-Butyl Ether.
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Some questions for you to text your expertise in the topic:-
What is Y in the following reactions?

A
B
C
D
(A) Tert butyl methyl ether is not prepared by the reaction of tert butyl bromide with sodium         methoxide.
(R) Sodium methoxide is a strong nucleophile.

A
Both A and R are true and R is the correct explanation to A
B
Both A and R are true and R is not the correctexplanation to A
C
A is true but R is false
D
A is false but R is true
The major product formed in the given reaction is:
A
B
C
D