CBSE Class 12 Chemistry Revision Notes Chapter 11
Class 12 Chemistry Chapter 11 Notes: Alcohol Phenol & Ethers
The Class 12 Chemistry Chapter 11 is about Alcohol Phenol and Ethers. This chapter discusses alcohols, phenols, ethers’ preparation, properties, and chemical reactions. This chapter includes some of the most fundamental topics of Organic Chemistry that have broad applications in the industries. When -OH group atoms form a bond with saturated carbon atoms, alcohol is synthesized. So, if the dehydration of alcohol takes place, ether is formed. In this unit, you will understand how these compounds are connected. In addition, there are three different types of alcohols- Monohydric, Dihydric, and Trihydric alcohols. All three are classified based on their -OH groups. Monohydric, dihydric, and trihydric alcohols consist of one -OH group, two -OH groups, and three -OH groups, respectively.
In this chapter, students will learn about these different types of alcohols, phenols, and ethers.
Alcohols and phenols have multiple applications in daily life and the industry, and alcohol comprises one or more hydroxyl (OH) groups. Moreover, the attachment of this particular group is to the carbon atom(s). Also, ether is simply an important class of organic compounds.
Alcohols are compounds with a hydroxyl group (- OH) attached to a saturated carbon atom. Enols are compounds with a hydroxyl group combined with an unsaturated carbon atom of a double bond. The saturated carbon can be alkyl, alkynyl, alkenyl, cycloalkyl, or benzyl. On the other hand, a hydroxyl group is connected to a benzene ring. Phenols are the name shown for these compounds.
Alcohol is used in both industries and everyday life:
- Ethanol, for example, is a familiar spirit used to polish wooden furniture.
- Sugar, cotton, and paper are composed of compounds that contain groups.
- Phenols are found in essential polymers, including bakelite and pharmaceuticals such as aspirin.
- Ethers are generally used as anesthetics and solvents.
Generally, in alcohols, the group’s oxygen is connected with carbon by a sigma bond formed by the overlap of an sp hybridized orbital of carbon with an sp hybridized orbital of oxygen. The following figure depicts the structural aspects of methanol, phenol, and methoxymethane.
CBSE Class 12 Chemistry Chapter 11 Notes explain the Chemistry of three compounds: alcohols, phenols, and ethers. Alcohol and phenols are formed when a hydrogen atom is in a hydrocarbon. Aliphatic and aromatic, respectively, are replaced by the -OH group. Substituting a hydrogen atom in a hydrocarbon with an alkoxy group(R-O/ Ar-O) yields another class of compounds known as ethers.
Classification of Alcohol Phenol and Ether:
As described in the Class 12 Chemistry Chapter 11 Notes, Alcohol and phenols may be classified as mono, di, tri, or polyhydric compounds depending upon the number of -OH groups respectively in their structures, as shown below:
- Based on the number of hydroxyl groups connected, alcohols can be classified into three types.
They contain one -OH group. Example, CH3CH2-OH
They contain two -OH groups. Example 1,2-Ethanol.
They contain three -OH groups. Example 1,2,3-Propantriol.
- Depending on the number of carbon atoms directly connected to the carbon bonded with the -OH group, alcohols can be distinguished into three types.
- Primary alcohols: One carbon atom is directly attached.
- Secondary alcohols: Two carbon atoms are directly attached.
- Tertiary alcohol: Three carbon atoms are directly attached.
The -OH groups are attached to an sp3 hybridized carbon next to the c-c double bond in these alcohols.
The OH group is attached to a benzylic carbon atom in these alcohols.
Compounds containing Csp2-OH bond
These alcohol contain an OH group bonded to a carbon-carbon double bond, i.e., vinylic carbon or aryl carbon. Ex vinylic alcohol.
Students may refer to the CBSE Class 12 Chemistry Chapter 11 study materials at the Extramarks website.
Classification of Phenol:
As stated in the Chemistry Class 12 Chapter 11 Notes, Phenols can be classified in three ways based on the number of hydroxyl groups attached.
- Monohydric phenols:
They contain one -OH group.
- Dihydric phenols:
They contain two -OH groups. They may be ortho-, meta- or para- derivatives.
- Trihydric phenols:
They contain three -OH groups.
Besides the Class 12 Chemistry Chapter 11 Notes, students are recommended to refer to various study materials such as NCERT Solutions and CBSE Revision Notes for a more detailed explanation, all available at the Extramarks website.
Classification of Ether:
Based on the type of the alkyl or aryl groups attached to the oxygen atom in ether, it can be classified into two ways:
- Symmetrical Ether:
Also shown as the simple ether, the alkyl or aryl group combined on either side of the oxygen atoms are the same. Examples are CH3OCH3, C2H5OC2H5, etc.
- Unsymmetrical ether:
Also known as the mixed, the alkyl or the aryl group combined on either side of the oxygen atoms are not the same. Examples are CH3OC2H5, C2H5OC6H5, etc.
Practice NCERT questions and answers on alcohol phenols and ether to better understand the topic. Refer to Class 12 Chemistry Chapter 11 Notes and the Extramark app to learn more about this concept and other related topics.
The common name of alcohol is derived from the common name of the alkyl group and adding the word alcohol to it.
The IUPAC name of alcohol is derived from the name of the alkane, and adding the suffix ‘ol’ as the letter ‘e’ of the alkane is dropped.
CH3OH methane + ol = Methanol
Cyclic alcohols are named using cyclo and considering the hydroxyl group attached to C1.
The most straightforward hydroxy derivative of benzene is phenol. It is its common name and is accepted in the IUPAC name also.
Dihydroxy benzene derivatives are named as 1,2-, 1,3- and 1,4- benzenediol.
General names of others are derived from the names of alkyl or aryl groups written as different words in alphabetical order and adding the word ether at the end. Example: CH3OC2H5 is ethyl methyl ether.
Alcohols and phenol:
Preparation of Alcohols:
Under this section of Class 12 Chemistry Chapter 11 Notes, students learn the alcohol preparation by following methods.
- Hydrolysis of Halides:
Alkyl halides, when boiled with an aqueous solution of an alkali hydroxide(KOH), give alcohol through a nucleophilic substitution mechanism.
R-X + KOH → R-OH + KX
This standard procedure produces primary and secondary alcohols. Glycerol can be synthesized from propylene by a series of reactions, including the hydrolysis of a halide as one step in the process.
- Hydration of Alkenes:
Direct hydration takes place by adding water in the presence of a catalyst.
Indirect addition of water is achieved by adding sulphuric acid to an alkane, followed by hydrolysis of the alkyl hydrogen sulfate.
- By reducing aldehyde and ketones:
Whenever we reduce aldehyde or ketones in reducing agents like Ni, Pd, Pt, LiAlH4, etc., we get alcohol.
Examples: CH3CHO + H2→ CH3CH2OH (ethanal changes into ethanol)
We can’t produce tertiary alcohol by this method.
- By reduction of carboxylic acid:
Whenever we reduce carboxylic acid in the presence of a reducing agent, it forms respective alcohol, as shown below:
RCOOH + H2→ RCH2OH
CH3COOH + H2→ CH3CH2OH (Ethanoic acid convert into ethanol)
- Hydroboration of Alkenes:
When treated with diborane, Alkenes from alkyl boranes, R3B. Alkylboranes, on oxidation with alkaline hydrogen peroxide, form alcohol.
It is significant to note that this process always leads to anti-Markovnikov’s addition of water to alkenes.
- Grignard Synthesis:
As explained in our Class 12 Chemistry Chapter 11 Notes, all types of alcohols (primary, secondary and tertiary) can be synthesized from the Grignard reagents by combining with suitable carbonyl compounds.
The reaction of the Grignard reagent with formaldehyde leads to primary alcohols with aldehydes. Also, formaldehyde yields secondary alcohols, and ketones give tertiary alcohols.
Preparation of Phenol (Carbolic acid): C6H6O
The following methods can synthesize phenols:
- From sulphonic acids (by alkali fusion of sodium benzene sulphonate):
This is the first commercial method for the synthesis of phenol. Sodium benzene sulphonate is fused with sodium hydroxide at 573K to produce sodium phenoxide, which upon acidification, yields phenol.
Synthesis of Phenols From Sulfonic Acids and haloarenes
- From diazonium salts (by the hydrolysis of diazonium salt-laboratory method)
When a diazonium salt solution is steam distilled or is added to boiling oil. H2SO4 forms phenol.
Synthesis of Phenols From Diazonium Salts
- From Cumene:
Phenol is synthesized from the hydrocarbon cumene. This Cumene(isopropylbenzene) is oxidized in the presence of air(oxygen) to cumene hydroperoxide. It is changed into phenol and acetone by reacting it with dil acid.
Alcohol and phenols are water-soluble due to their forming hydrogen bonds with water. The solubility decreases with an enhancement in the size of the hydrophobic group. Because of the same reason, their boiling points are more significant than corresponding compounds of similar molecular mass except for carboxylic acids. They are polar and protic.
The acidity of alcohols and phenols as explained in our Class 12 Chemistry Chapter 11 Notes:
- Reaction with metals:
Alcohol and phenols interact with active metals such as sodium(Na), potassium(K), and aluminum (Al) to yield corresponding alkoxide, phenoxide, and hydrogen gas.
- The acidity of Alcohols:
The polar nature of the OH bond causes the acidic character of alcohols. An electron-releasing group enhances electron density on oxygen, tending to decrease the polarity of the OH bond. Alcohol decreases the acid strength. Hence, the acidic strength follows the acidity order is Primary > Secondary> Tertiary.
Alcohols are weaker acids than water.
- The acidity of phenols:
Because the phenoxide ion is stabilized through resonance, phenol is more acidic than alcohol. The presence of an electron-withdrawing group raises phenol’s acidity by stabilizing the phenoxide ion. In contrast, the presence of an electron-releasing group lowers phenol’s acidity by destabilizing the phenoxide ion.
Alcohols and phenol react with carboxylic acid, acid chloride, and anhydrides to form esters. With carboxylic acids, esterification is carried with a small amount of concentrated Sulphuric acid.
Reaction with hydrogen halides:
Alcohols react with HX to form alkyl halides.
ROH + HX → RX + H2O
CH3OH + HCl → CH3Cl + H2O
Reaction with PCl3 and PCl5:
3 ROH + PCl3 → 3RCl + H3PO3
ROH + PCl5 → RCl + HCl +POCl3
Reaction with SOCl2:
ROH + SOCl2 → RCl + SO2 + HCl
Alcohols undergo dehydration (removing a water molecule) to form alkene when reacting with a protic acid—for Example, conc sulphuric acid or H3PO4 or Al2O3.
The oxidation state of the carbon-bearing -OH group is (-2), so it can be oxidized to aldehyde (oxidation state=0) and carboxylic acids (oxidation state= +2) by the use of suitable reagents.
Reactions of phenol:
The phenols show the following reactions:
As described in the Class 12 Chemistry Chapter 11 Notes, when phenol is treated with bromine in a solvent of low polarities such as chloroform or carbon disulfide, and at low temperature, monobromo phenols are formed.
When phenol is reacted with bromine water, 2,4,6 tribromophenol is formed as white ppt.
With dilute nitric acid at (298K) low temperature, phenol yields a mixture of ortho and para nitrophenols.
On treatment with chloroform in the presence of sodium hydroxide(NaOH), a -CHO group is attached at the ortho position of the benzene ring. This reaction is called the Reimer Tiemann reaction. The intermediate substituted benzyl chloride is hydrolyzed in the presence of alkali to synthesize salicylaldehyde.
When treated with sodium hydroxide, phenol gives a phenoxide ion, which is more reactive than phenol. Hence it undergoes an electrophilic substitution reaction with CO2, a weak electrophile. Ortho hydroxybenzoic acid is developed as the primary product.
The reaction of phenol with zinc dust:
Phenol is converted to benzene on heating with zinc dust.
Phenol converts into benzoquinone by applying solid oxidizing agents(chromic acid). In the presence of air, phenols are steadily oxidized to the dark-colored mixture containing quinones.
Some commercially important alcohols as explained in Class 12 Chemistry Chapter 11 Notes:
- Methanol (CH3OH):
Methanol, also known as ‘Wood-spirit, was produced by the destructive distillation of wood. It is a transparent liquid with no visible color. It reaches a temperature of 337 Fahrenheit when it boils. It is highly poisonous. Even a few doses can cause blindness, and excessive doses can result in death. Methanol is used as a solvent in paints, and varnishes, and chiefly for making formaldehyde.
Today, most methanol is produced by catalytic hydrogenation of carbon monoxide at high pressure and temperature and in the presence of a ZnO-Cr2O3 catalyst.
Paints, varnishes, and various products use it as a solvent. It can be used to make formaldehyde.
- Ethanol (C2H5OH):
Ethanol is obtained commercially by fermentation. The oldest method is from sugars. It is called a denatured spirit when combined with copper sulfate (CuSO4) and pyridine. It is a colorless liquid having a boiling point of 351 K.
Commercially, it is obtained by fermentation of sugars. The sugar is molasses.
- Glucose and fructose undergo fermentation in the presence of zymase, which is found in yeast.
- In winemaking, grapes are the source of sugars and yeast. As grapes ripen, the number of sugar increases, and yeast grows on the outer skin. When grapes are crushed, sugar and the enzymes come in contact, and fermentation occurs.
- Fermentation occurs in anaerobic conditions, i.e. in the absence of air. Carbon Dioxide is released during fermentation.
It is a suitable solvent for sterilizing surgical tools in laboratories and hospitals.
Preparation of ether by :
(i)By intermolecular dehydration of alcohols:
Alcohols undergo dehydration in the presence of protic acid.
(ii) Williamson synthesis:
It is a crucial method to prepare all types of ether. An alkyl halide is allowed to interact with sodium alkoxide.
R-X + R-O-Na yields→ R-O-R + Na X
Physical properties of ethers:
- Due to the large size of the alkyl group, the ROR bond angle in ethers is large (> 110 degrees); therefore, ethers’ C-O bonds are polar and have a net dipole moment.
- Their boiling points equal alkanes with the same molecular weights, although lower than alcohols.
- Ethers don’t have Hydrogen-bonding.
Ether miscibility with water is precisely that of alcohols of a similar molar mass. It’s because others, like alcohols, can make Hydrogen-bonds with water.
Students are advised to refer to the NCERT Class 12 Chemistry Chapter 11 Notes, available at the Extramarks website, for a more detailed explanation of the above topics.
Chemical properties of ethers:
- Cleavage of C-O bonds in ethers:
Ethers are the least reactive among other functional groups due to low polarity. With strong acids, they form alkyl halide and alcohols by C-O bond cleavage.
R-O-R + HX → RX + R-OH
R-OH + HX → R-X + H2O
- Electrophilic substitution reactions:
Aryl ethers show the reactions like phenols as -OR is also an activating group. The electrophilic substitution shown by aryl ethers is halogenation, nitration, and Friedel crafts reaction.
Phenyl alkyl ethers undergo usual halogenation in the benzene ring. For example, Anisole undergoes bromination with bromine in ethanoic acid even without an iron bromide catalyst. It is due to the activation of benzene rings by the methoxy group. Para isomer is obtained in 90% yield.
- Friedel craft’s reaction:
Anisole undergoes Friedel crafts reaction, i.e., the alkyl or acyl groups are introduced at ortho and para positions by reacting with an alkyl and acyl halide in anhydrous aluminum chloride (lewis acid) as a catalyst.
Anisole interacts with concentrated sulphuric and nitric acids to yield a mixture of ortho and para nitro anisole.
Class 12 Chemistry Chapter 11 Alcohol Phenol & Ethers is a comparatively difficult chapter. Students need to understand the theory properly to get a good hold of the subject. Chapter 11 is really crucial and many questions are repeatedly asked in a variety of entrance and competitive examinations like VITEEE, BITSAT, JEE Main, NEET, etc.
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Class 12 Chemistry Chapter 11 Notes: Exercise & Solutions
Extramarks Class 12 Chemistry Chapter 11 Notes also include a lot of exercises and their solved answers are based on NCERT books. Every exercise is compiled to add more value to the chapter. Students may refer to various study materials such as revision notes, past year question papers, Important Questions, and more about NCERT Solutions on Extramarks’ website.
Class 12 Chemistry Chapter 11 Notes are explained in detail by the Extramarks experienced faculty. In addition to Chapter 11, students can access NCERT Solutions for the entire Chemistry syllabus of Class 12.
Students can click on the links provided below to refer to the complete set of questions and answers covered in the NCERT textbook:
- Chapter 11: Exercise 11.1 Solutions
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- Chapter 11: Exercise 11.12 Solutions
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NCERT Exemplar Class 12 Chemistry Chapter 11
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Key Features of CBSE Solutions Class 12 Chemistry Chapter 11 Notes
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Ethers are used as cleansing agents in our daily life. For example, Glycol ether is used as a cleaner for window glasses, carpets, floors, etc. Ether is used as an anesthetic in surgery, as a cooling agent, and inert solvent in Grignard reagents.Vapors of certain ethers are used as insecticides, miticides, and fumigants for soil.