Maharashtra Board Class 12 Chemistry Chapter 11 Alcohols Phenols And Ethers PDF Download

11. Alcohols, Phenols And Ethers

11.1 Introduction

Alcohols are organic compounds whose molecules contain hydroxyl group, (-OH) attached to a saturated carbon atom.

Hydroxyl group can also be present in aromatic compounds. There are two types of aromatic hydroxy compounds: phenols and aromatic alcohols. Phenols contain a hydroxyl group directly attached to the carbon atom of benzene ring. When the hydroxyl group is present in the side chain of aromatic ring, the compound is termed as aromatic alcohol.

Ethers are compounds which contain an oxygen atom bonded to two alkyl groups or two aryl groups or one alkyl and one aryl group. Ethers are organic oxides. Ethers are considered as anhydrides of alcohols.

Epoxides are cyclic ethers in which the ethereal oxygen is a part of a three membered ring.

11.2 Classification

11.2.1 Mono, Di, Tri And Polyhydric Compounds

Alcohols and phenols are classified as mono, di-, tri, or polyhydric compounds on the basis of one, two, three or more hydroxyl groups present in their molecules.

Monohydric alcohols are further classified on the basis of hybridisation state of the carbon atom to which hydroxyl group is attached.

a. Alcohols containing sp\(^3\) C - OH bond: In these alcohols -OH group is attached to a sp\(^3\) hybridised carbon atom of alkyl group. These alcohols are further classified as primary (1\(^{\circ}\)), secondary (2\(^{\circ}\)) and tertiary (3\(^{\circ}\)) alcohols in which -OH group is attached to primary, secondary and tertiary carbon atom respectively.

b. Alcohols containing sp\(^2\) C - OH bonds: In these alcohols -OH group is attached to a sp\(^2\) hybridised carbon atom which is part of a carbon-carbon double bond. These alcohols are known as vinylic alcohols. For example CH\(_2\) = CH - OH (Vinyl alcohol)

11.2.2 Classification Of Ethers

Ethers are classified as symmetrical ethers (simple ethers) or unsymmetrical ethers (mixed ethers) depending on whether the two alkyl/aryl groups bonded to oxygen atom are same or different respectively.

Each of these three types of alcohols can also be either allylic or benzylic if the sp\(^3\) carbon carrying -OH is further bonded to sp\(^2\) carbon.

Allylic alcohols: In this type of alcohols -OH group is attached to sp\(^3\) hybridised carbon atom which is further bonded to a carbon-carbon double bond. Allylic alcohol may be primary, secondary or tertiary.

Benzylic alcohols: In this type of alcohols -OH group is attached to sp\(^3\) hybridised carbon atom which is further bonded to an aromatic ring. Benzylic alcohol may be primary, secondary or tertiary.

Teacher's Note

Alcohols are very common in our daily life. For example, we drink water mixed with ethanol, and we use phenol in antiseptic solutions. Understanding these compounds helps us know the chemistry behind the things we use every day.

Exam Trick

Remember: Primary alcohol has one R group, secondary has two R groups, and tertiary has three R groups attached to the carbon with -OH. Think of it like students in a class - primary is alone, secondary is with a partner, and tertiary is in a group of three.

Points To Remember

Alcohols have -OH group attached to saturated carbon atoms.
Phenols have -OH group attached to benzene ring.
Ethers have oxygen bonded to two alkyl or aryl groups.
Monohydric means one -OH group, dihydric means two -OH groups.
Primary, secondary, and tertiary alcohols differ in the number of carbon atoms bonded to the carbon carrying -OH.

11.3 Nomenclature

11.3.1 Alcohols

There are three systems of nomenclature of monohydric alcohols.

a. Common/Trivial Names: The common or trivial names of alcohols are obtained by adding word alcohol after the name of alkyl group bonded to -OH. Names of higher alkyl groups also include prefixes like normal, iso, secondary, tertiary.

b. Carbinol System: In this system alcohols are considered as derivatives of methyl alcohol which is called carbinol. The alkyl group attached to the carbon carrying -OH group are named in alphabetical order. Then the suffix carbinol is added.

c. IUPAC System: According to IUPAC system, alcohols are named as alkanols. The ending 'e' in the name of the parent alkane, alkene or alkyne is replaced by the suffix 'ol'. For naming polyhydric alcohol, 'e' in the ending of alkane is retained, the ending 'ol' is added and number of -OH groups is indicated by prefix di, tri, etc., before 'ol'. The positions of -OH groups are indicated by appropriate locants.

Teacher's Note

The IUPAC system is like a universal language for chemistry. Just like we have one name for a person in their passport, we have one IUPAC name for each compound. This helps scientists all over the world understand each other.

Exam Trick

Remember: In IUPAC naming, always find the longest carbon chain with -OH group. Number the chain so that -OH gets the lowest number. This is like finding the main road in a city and numbering houses on it.

Points To Remember

Common names use "alcohol" after the alkyl group name.
Carbinol system is based on methanol as the parent compound.
IUPAC names use "ol" suffix and give the position of -OH group.
For polyhydric alcohols, use prefixes di-, tri-, etc.
Always number the carbon chain to give -OH the lowest number.

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