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Alcohol, phenol, and ether are the different classes of organic compounds which are usually found in wide usage in an extensive range of industries and also for domestic purposes. Alcohol is naturally formed when a saturated carbon atom is bonded to a hydroxyl (-OH) group, also in chemical form. Phenol is another classification of Alcohol that is formed when a hydrogen atom in a benzene molecule is replaced by the chemical -OH group. Ether is another classification under Alcohol which is formed when an oxygen atom is connected to two alkyl or aryl groups.
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Key Terms: Organic chemistry, Alcohol, Phenol, hydroxyl groups, compounds, benzene, Hydrogen, Atom, Ether
Classification of Alcohol
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The Classification of Alcohol is dependant on the number of hydroxyl groups attached. On this basis, alcohol can be classified into three different types.
- Monohydric alcohols: These contain one -OH group. Example, CH3CH2-OH
- Dihydric alcohols: These contain two -OH groups. Example, 1,2-Ethanediol.
- Trihydric alcohols: These contain three -OH groups. Example 1,2,3-Propanetriol.
Classification of alcohol
The Classification of alcohol is also dependant on the different number of carbon atoms in a molecule that are bonded with the -OH group. On this basis, alcohol can be classified into three different types which are mentioned below.
- Primary alcohols: Here, one carbon atom is directly attached to the -OH bond.
- Secondary alcohols: Here, two carbon atoms are directly attached to the -OH bond.
- Tertiary alcohols: Here, three carbon atoms are directly attached to the -OH bond
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| Chapter Related Concepts | ||
|---|---|---|
| Ester Hydrolysis | Fehling Test | Iodoform Test |
| Hell-Volhard-Zelinsky Reaction | Friedel-Crafts acylation reaction | Butyric Acid |
| Resonance | Grignard Reagent | Enantiomers |
Preparation of Alcohol
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Some methods used in the preparation of alcohol are-
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Reduction of Carbonyl Compounds
Reduction of Carbonyl Compounds
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By Hydroboration-oxidation reaction
The hydroboration–oxidation reaction is a certain reaction where borane is added for the oxidation to take place. For example, the compound propan–1–ol is formed by making propene undergo the hydroboration–oxidation reaction. In the above-mentioned reaction, the reaction between propene and the compound diborane (BH3)2 takes place to form trialkyl borane which makes an additional product. This additional by-product is also oxidized to perform alcohol by hydrogen peroxide in the presence of aqueous sodium hydroxide.
By hydroboration–oxidation method: Diborane (BH3 )2 reacts with certain alkenes to give a by-product called trialkyl boranes as an additional product. This is oxidized to form alcohol by hydrogen peroxide in the presence of aqueous sodium hydroxide. The further adding of borane to the double bond takes place in such a way that the boron atom gets attached to the sp2 carbon carrying a greater number of hydrogen atoms. The alcohol formed looks as if it has been formed by the addition of water to the alkene in a way opposite to Markovnikov’s rule. The alcohol is obtained in this reaction in an excellent yield.
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Preparation of alcohol from Alkenes
Alcohols can also be prepared from alkenes by acid-catalyzed hydration. Alkenes react with the water present and the acid acts as a catalyst and aids the chemical reaction to form certain alcohols. In the case of unsymmetrical alkenes, the additional reaction takes place according to Markovnikov’s rule. The reaction occurs in 3 steps of mechanism which are such:
Step 1: The Protonation of certain alkene to form carbocation by an electrophilic attack.
H3O + H2O + H+ → H3O +
Step 2: Nucleophilic attack of water on carbocation.
Step 3: Deprotonation to form alcohol.
And many others
Preparation of alcohol from Alkenes
Classification of Phenol
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On the basis of the different number of hydroxyl groups attached, the phenols can be classified further into three types.
- Monohydric phenols: These contain one -OH group.
- Dihydric phenols: These contain two -OH groups. These may be ortho-, meta- or para- derivative.
- Trihydric phenols: These contain three -OH groups.
Classification of Phenol
Preparation of Phenol
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- Diazonium Salts
- Cumene
- Benzene Sulphonic Acid
- Haloarenes
Classification of Ether
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The Classification is dependant on the type of the alkyl or aryl groups attached to the oxygen atom in ether group, thus it can be classified into two types.
- Symmetrical ether: This is also known as a simple ether. Here, the alkyl or aryl group attached on the different sides of the oxygen atoms are the same. Examples are CH3OCH3, C2H5OC2H5, etc.
- Unsymmetrical ether: This is also known as mixed either. Here, the alkyl or the aryl group attached on the different sides of the oxygen atoms, are not the same. Examples are CH3OC2H5, C2H5OC6H5, etc.
Preparation of Ethers
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- Dehydration of Alcohol
- Williamson synthesis
An important method that is performed in labs for the preparation of symmetrical and unsymmetrical ethers is known as the Williamson synthesis. In this methodology, an alkyl halide is allowed to react with sodium alkoxide. The ethers which contain certain substituted alkyl groups (secondary or tertiary) can also be prepared by this method. The reaction contains the SN2 attack of an alkoxide ion on another primary alkyl halide.
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Sample Questions
Ques. Why propanol has a higher boiling point than butane and hydrocarbon? (2 marks)
Ans. The presence of the compound –OH group makes the alcohol type Propanol undergo intermolecular H-bonding. Butane, while on the other hand does not have the same privilege.
Hence, to break the strong intermolecular hydrogen bonds, additional energy would be required. This is also the reason why hydrocarbon butane has a lower boiling point than propanol.
Ques. Why are certain alcohols subsequently more soluble in water than the hydrocarbons of comparable molecular masses? (2 marks)
Ans. Due to the presence of the group of atoms in the –OH group, alcohols usually form H–bonds with water.
Hence, due to this reason, the alcohols are more soluble, than hydrocarbons of comparable molecular masses, in water.
Ques. Which isomer will be steam volatile before the steam distillation process used to separate a mixture of para and ortho nitrophenols? (2 marks)
Ans. Intramolecular H–bonding is present in o–nitrophenol & p–nitrophenol. In p–nitrophenol, due to the preferred existence of intermolecular bonding, the molecules are also strongly associated Therefore, o – nitrophenol is steam volatile.
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