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Here, you can learn the NCERT Class 12 Books Chemistry Chapter 11- Alcohols, Phenols and Ethers. Moreover, you can get the links for other chapters to download the links.
You have learnt that substitution of one or more hydrogen atom(s) from a hydrocarbon by another atom or a group of atoms result in the formation of an entirely new compound having altogether different properties and applications.
Alcohols and phenols are formed when a hydrogen atom in a hydrocarbon, aliphatic and aromatic respectively, is replaced by –OH group.
These classes of compounds find wide applications in industry as well as in day-to-day life.
For instance, have you ever noticed that 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.
Just think of life without paper; no note-books, books, newspapers, currency notes, cheques, certificates, etc.
The magazines carrying beautiful photographs and interesting stories would disappear from our life.
It would have been really a different world.
Alcohols, Phenols and Ethers
An alcohol contains one or more hydroxyl (OH) group(s) directly attached to carbon atom(s), of an aliphatic system (CH3OH) while a phenol contains –OH group(s) directly attached to carbon atom(s) of an aromatic system (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, CH3OCH3 (dimethyl ether). You may also visualise ethers as compounds formed by substituting the hydrogen atom of hydroxyl group of an alcohol or phenol by an alkyl or aryl group.
In this unit, we shall discuss the chemistry of three classes of compounds, namely — alcohols, phenols and ethers.
The classification of compounds makes their study systematic and hence simpler.
Therefore, let us first learn how are alcohols, phenols and ethers classified?
Alcohols— Mono, Di, Tri or Polyhydric alcohols
Alcohols and phenols may be classified as mono–, di–, tri- or polyhydric compounds depending on whether they contain one, two, three or many hydroxyl groups respectively in their structures as given below:
Monohydric alcohols may be further classified according to the hybridisation of the carbon atom to which the hydroxyl group is attached.
(i) Compounds containing C 3− OH sp bond: In this class of alcohols, the –OH group is attached to an sp3 hybridised carbon atom of an alkyl group. They are further classified as follows:
Primary, secondary and tertiary alcohols: In these three types of alcohols, the –OH group is attached to primary, secondary and tertiary carbon atom, respectively as depicted below:
Allylic alcohols: In these alcohols, the —OH group is attached to a sp3 hybridised carbon adjacent to the carbon-carbon double bond, that is to an allylic carbon. For example
Benzylic alcohols: In these alcohols, the —OH group is attached to a sp3—hybridised carbon atom next to an aromatic ring. For example.
Allylic and benzylic alcohols may be primary, secondary or tertiary.
(ii) Compounds containing C 2− OH sp bond: These alcohols contain —OH group bonded to a carbon-carbon double bond, i.e., to a vinylic carbon or to an aryl carbon. These alcohols are also known as vinylic alcohols.
Vinylic alcohol: CH2 = CH – OH
Phenols— Mono, Di and trihydric phenols
Ethers are classified as simple or symmetrical, if the alkyl or aryl groups attached to the oxygen atom are the same, and mixed or unsymmetrical, if the two groups are different. Diethyl ether, C2H5OC2H5, is a symmetrical ether whereas C2H5OCH3 and C2H5OC6H5 are unsymmetrical ethers.
Nomenclature(a) Alcohols: The common name of an alcohol is derived from the common name of the alkyl group and adding the word alcohol to it. For example, CH3OH is methyl alcohol.
According to IUPAC system (Unit 12, Class XI), the name of an alcohol is derived from the name of the alkane from which the alcohol is derived, by substituting ‘e’ of alkane with the suffix ‘ol’. The position of substituents are indicated by numerals. For this, the longest carbon chain (parent chain) is numbered starting at the end nearest to the hydroxyl group. The positions of the –OH group and other substituents are indicated by using the numbers of carbon atoms to which these are
attached. For naming polyhydric alcohols, the ‘e’ of alkane is retained and the ending ‘ol’ is added. The number of –OH groups is indicated by adding the multiplicative prefix, di, tri, etc., before ‘ol’. The positions of –OH groups are indicated by appropriate locants, e.g., HO–CH2–CH2–OH is named as ethane–1, 2-diol. Table 11.1 gives common and IUPAC names of a few alcohols as examples.
Cyclic alcohols are named using the prefix cyclo and considering the —OH group attached to C–1.
b) Phenols: The simplest hydroxy derivative of benzene is phenol. It is its common name and also an accepted IUPAC name. As structure of phenol involves a benzene ring, in its substituted compounds the terms ortho (1,2- disubstituted), meta (1,3-disubstituted) and para (1,4-disubstituted) are often used in the common names.
(c) Ethers: Common names of ethers are derived from the names of alkyl/ aryl groups written as separate words in alphabetical order and adding the word ‘ether’ at the end. For example, CH3OC2H5 is ethylmethyl ether.
If both the alkyl groups are the same, the prefix ‘di’ is added before the alkyl group. For example, C2H5OC2H5 is diethyl ether. According to IUPAC system of nomenclature, ethers are regarded as hydrocarbon derivatives in which a hydrogen atom is replaced by an –OR or –OAr group, where R and Ar represent alkyl and aryl groups, respectively. The larger (R) group is chosen as the parent hydrocarbon. The names of a few ethers are given as examples in Table 11.2.
NCERT Class 12 Books Chemistry Chapter 11- Alcohols, Phenols and Ethers- PDF Download
Unit 11: Alcohols, Phenols and Ethers
अध्याय 11: एल्कोहल, फिनॉल एवं ईथर
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