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1 Solutions 2 Electrochemistry 3 Chemical Kinetics 4 The d-and f-Block Elements 5 Coordination Compounds 6 Haloalkanes and Haloarenes 7 Alcohols, Phenols and Ethers 8 Aldehydes, Ketones and Carboxylic Acids 9 Amines 10 Biomolecules

7 Alcohols, Phenols and Ethers

7.1 Classification of Alcohols, Phenols and Ethers 7.2 Nomenclature 7.3 Structures of Functional Groups 7.4 Alcohols and Phenols 7.5 Some Commercially Important Alcohols 7.6 Ethers

Alcohols and Phenols

NCERT Reference Chapter 7 – Alcohols, Phenols and Ethers – Pages 174–184

Quick Notes

  • Alcohols are prepared from alkenes, carbonyl compounds, and Grignard reagents.
  • Phenols are prepared from haloarenes, benzenesulphonic acid, diazonium salts, and cumene.
  • Boiling points increase with hydrogen bonding and molecular mass.
  • Solubility depends on the number of –OH groups and chain length.
  • Reactions of alcohols and phenols involve:
    • Cleavage of O–H bond (acidity, esterification)
    • Cleavage of C–O bond (halide substitution, dehydration, oxidation)
    • Electrophilic substitution in phenols (e.g. nitration, halogenation)
    • Special reactions: Kolbe’s, Reimer-Tiemann, oxidation, zinc dust

Full Notes

Alcohols can be synthesized through multiple pathways involving addition, reduction, and organometallic reagents.

Alcohols From Alkenes

Water is added across the double bond to form alcohols.

Acid-Catalysed Hydration

NCERT Class 12 Chemistry acid-catalysed hydration of alkenes to alcohols diagram with dilute H2SO4 and carbocation intermediate.

Water adds to alkenes in the presence of dilute H2SO4 via carbocation intermediates.

Follows an electrophilic addition mechanism and Markovnikov's rule.

Mechanism:

NCERT Class 12 Chemistry stepwise mechanism for acid-catalysed hydration of propene to propan-2-ol.

Example Hydration of propene

CH3–CH=CH2 + H2O (H+) → CH3–CH(OH)–CH3

Hydroboration–Oxidation

A two-step reaction that avoids rearrangement and gives anti-Markovnikov product.

NCERT Class 12 Chemistry hydroboration–oxidation of alkenes using BH3·THF followed by H2O2/NaOH to form alcohols anti-Markovnikov.

Uses BH3•THF followed by H2O2/NaOH.

Example Ethene to ethanol

CH2=CH2 → CH3–CH2OH

Alcohols From Carbonyl Compounds

Carbonyl groups undergo reduction to yield alcohols.

Reduction using NaBH4 or LiAlH4

Aldehydes form primary alcohols and ketones form secondary alcohols.

NCERT Class 12 Chemistry reduction of aldehydes and ketones to alcohols using NaBH4 or LiAlH4.

LiAlH4 is a more powerful reducing agent than NaBH4, because of this if LiAlH4 is used and no water can be present and the reaction must be carried out in dry ether.

Examples Typical reductions

Photo of Matt
Matt’s exam tip

Remember reduction in organic chemistry is the gaining of a carbon-hydrogen bond. To provide the hydrogen needed, we use reducing agents (such as NaBH4 and LiAlH4) and show hydrogen from a reducing agent in equations as [H].

Reduction of Carboxylic Acids

NCERT Class 12 Chemistry LiAlH4 reduction of carboxylic acids to primary alcohols.

Reagent: LiAlH4 (only)

LiAlH4 is strong enough to reduce acids to primary alcohols, NaBH4 can’t.

LiAlH4 is expensive, so it is typically reserved for the preparation of special chemicals. On a commercial scale, carboxylic acids are first converted to esters (see Section 7.4.4), which are then reduced to alcohols by catalytic hydrogenation – that is, using hydrogen gas in the presence of a catalyst.

Example Ethanoic acid to ethanol

CH3COOH + 4[H] → CH3CH2OH + H2O

Catalytic Hydrogenation

Involves H2 gas and catalysts such as Pd to reduce the C=O bond.

NCERT Class 12 Chemistry catalytic hydrogenation of aldehydes to primary alcohols using H2 and Pd.

Example Ethanal to ethanol

CH3CHO + H2 → CH3CH2OH

From Grignard Reagents

Grignard reagents react with carbonyl compounds to give alcohols after hydrolysis.

NCERT Class 12 Chemistry summary chart of Grignard reagent additions: formaldehyde gives 1° alcohol, aldehydes 2° alcohol, ketones 3° alcohol.

Example Propan-2-ol from CH3MgBr

CH3MgBr + CH3CHO → CH3CH(OH)CH3

Preparation of Phenols

Phenols are typically obtained from aromatic compounds through substitution or hydrolysis reactions.

Phenols From Haloarenes

Nucleophilic substitution of halogen by –OH under harsh conditions.

NCERT Class 12 Chemistry conversion of chlorobenzene to phenol using aqueous NaOH at high temperature and pressure.

Reagent: NaOH, 623 K, 300 atm
More efficient with electron-withdrawing groups (e.g., NO2) at ortho/para positions.

Example Chlorobenzene to phenol

C6H5Cl → C6H5OH

Phenols From Benzenesulphonic Acid

Alkaline fusion followed by acidification gives phenol.

NCERT Class 12 Chemistry alkaline fusion of benzenesulphonic acid to sodium phenoxide followed by acidification to phenol.

Phenols From Diazonium Salts

Thermal decomposition of diazonium salt yields phenol.

NCERT Class 12 Chemistry hydrolysis of benzenediazonium chloride to phenol with loss of N2.

Reagent: H2O or Cu2O/HCl

Example Benzenediazonium chloride

C6H5N2+Cl + H2O → C6H5OH + N2 + HCl

Phenols From Cumene

Industrial method involving oxidation of cumene and hydrolysis.

NCERT Class 12 Chemistry oxidation of cumene to cumene hydroperoxide and acid hydrolysis to phenol and acetone.

Physical Properties

Boiling Points
Due to hydrogen bonding, alcohols and phenols have higher boiling points than hydrocarbons of similar size.

Intermolecular Hydrogen Bonding:

Alcohols and phenols have an –OH group capable of forming strong hydrogen bonds with each other.

NCERT Class 12 Chemistry depiction of intermolecular hydrogen bonding between alcohol or phenol molecules.

These hydrogen bonds raise their boiling points significantly.

Solubility

Hydrogen bonding makes shorter chain alcohols and phenols water-soluble.

NCERT Class 12 Chemistry diagram showing hydrogen bonding of ethanol with water explaining solubility.

Solubility decreases with increasing alkyl group size. Polyhydric alcohols (those with more than one OH group) are more soluble than monohydric ones.

Chemical Reactions

Alcohols are versatile and can behave as Nucleophiles (electron pair donors) and Electrophiles (electron pair acceptors after protonation)

Alcohols as Nucleophiles:

The O–H bond is broken.

The lone pair on oxygen attacks an electrophile (e.g. a carbon with a leaving group).

NCERT Class 12 Chemistry schematic of alcohol acting as a nucleophile to form an ether linkage after attacking an electrophilic carbon.

Protonated Alcohols as Electrophiles:

The C–O bond is broken after protonation of the alcohol.

The alcohol becomes –OH2+, a good leaving group.

NCERT Class 12 Chemistry scheme showing alcohol protonation to form a good leaving group and substitution by bromide.

Reactions Involving Cleavage of O–H Bond

Reaction with Metals:

Alcohols and phenols react with Na, K, Al to form alkoxides/phenoxides + H2.

NCERT Class 12 Chemistry reaction of sodium metal with alcohol to give sodium alkoxide and hydrogen gas.

2R–OH + 2Na → 2R–ONa + H2

Phenol + Na → Sodium phenoxide + H2

NCERT Class 12 Chemistry sodium reacting with phenol to form sodium phenoxide and hydrogen gas.

Reaction with Aqueous NaOH:

Phenols react with NaOH forming sodium phenoxide.

NCERT Class 12 Chemistry deprotonation of phenol by aqueous NaOH forming sodium phenoxide.

Alcohols do not react (less acidic).

Nature of Acidity:

Alcohols & phenols are Brønsted acids (proton donors).

Acidity order (due to electron-donating groups reducing O–H polarity):
Primary > Secondary ≫ Tertiary

Comparison with Water:
Alcohols are weaker acids than water. This is because the alkoxide ion is a stronger base than OH. This can be seen between the reaction of an alkoxide ion and water, forming an alcohol (the conjugate acid of the alkoxide ion) and OH ions.

NCERT Class 12 Chemistry equilibrium showing alkoxide abstracting a proton from water to form alcohol and hydroxide.

Phenol Acidity:
Due to the sp2 carbon of benzene ring (electron withdrawing). Resonance stabilizes phenoxide ion → increases acidity.

Ionisation Comparison:

NCERT Class 12 Chemistry comparison of ionisation of alcohol vs phenol with resonance-stabilised phenoxide.

Substituent Effects:
Electron-withdrawing groups (e.g., –NO2) at ortho/para increase acidity. Electron-donating groups (e.g., –CH3) decrease acidity.

Reactions Involving Cleavage of C–O Bond (Alcohols only)

Reaction with HX (Lucas Test):

NCERT Class 12 Chemistry Lucas test converting alcohols to alkyl halides with conc. HCl and ZnCl2, showing tertiary reacting fastest.

ROH + HX → R–X + H2O
Lucas reagent: conc. HCl + ZnCl2.

Reaction with PX3:

ROH + PX3 → R–X (see class 12, section 6.4)

Dehydration to Alkenes:

NCERT Class 12 Chemistry dehydration of alcohols to alkenes using conc. acid or Al2O3 with heat.

Reagent: Conc. H2SO4 / H3PO4 / Al2O3 (heat)

Order of ease of dehydration: Tertiary > Secondary > Primary (conditions required to dehydrate get milder)

Mechanism (Ethanol example):

NCERT Class 12 Chemistry E1 dehydration mechanism of ethanol via protonation, carbocation and elimination to ethene.

Oxidation of Alcohols

Oxidation of alcohols involves the removal of hydrogen (dehydrogenation) or the addition of oxygen. It typically affects the O–H and C–H bonds on the carbon bearing the –OH group.

Primary alcohols (1°)

NCERT Class 12 Chemistry oxidation pathway for primary alcohols to aldehydes and then carboxylic acids with oxidising agents.

Secondary alcohols (2°)

NCERT Class 12 Chemistry oxidation of secondary alcohols to ketones using CrO3 or similar oxidants.

Tertiary alcohols (3°)

Do not oxidise easily because they lack a hydrogen atom on the carbon with the –OH group.

Under drastic conditions (e.g., strong oxidisers like KMnO4 at high temperatures), they undergo cleavage of C–C bonds, forming a mixture of carboxylic acids with smaller carbon chains.

Dehydrogenation (Catalytic oxidation at 573 K with Cu)

Dehydrogenation is used in laboratory preparation of aldehydes and ketones without over-oxidising the product.

Alcohol vapours are heated over copper:

NCERT Class 12 Chemistry catalytic dehydrogenation of alcohols over heated copper to form aldehydes or ketones.

Reactions of Phenols

Phenol is more reactive than benzene due to the lone pair on the oxygen delocalising into the π-system.

NCERT Class 12 Chemistry resonance structures showing lone pair donation from oxygen of phenol increasing ring electron density.

This increases electron density, activating the ring towards electrophilic substitution.

NCERT Class 12 Chemistry electron density map of phenol indicating activation at ortho and para positions.

Directing Effects of the –OH Group

The hydroxyl group activates the benzene ring and directs substitution to the ortho (2-), para (4-), and 6-positions.

NCERT Class 12 Chemistry directing effects of hydroxyl group on phenol favouring ortho and para substitution.

This explains the pattern of substitution.

Nitration:

With dilute nitric acid at low temperature (298 K), phenol yields a mixture of ortho and para nitrophenols.

NCERT Class 12 Chemistry nitration of phenol to give 2-nitrophenol and 4-nitrophenol under mild conditions.

The positional isomers can be separated by steam distillation because 2-nitrophenol (o-nitrophenol) is more volatile than 4-nitrophenol (p-nitrophenol).

This is due to intramolecular hydrogen bonding in 2-nitrophenol, which does not hinder volatility, while intermolecular hydrogen bonding in 4-nitrophenol leads to stronger molecular interactions, reducing its volatility.

NCERT Class 12 Chemistry comparison of intramolecular vs intermolecular hydrogen bonding in o-nitrophenol and p-nitrophenol explaining volatility.

When concentrated HNO3 is used, multiple substitutions occur and Picric acid (2,4,6-trinitrophenol) is formed.

Halogenation:

Phenol reacts with bromine to give different products depending on the reaction conditions used.

In CS2 and low temperatures, mono bromination occurs (only one Br gets substituted into the ring).

NCERT Class 12 Chemistry monobromination of phenol under controlled conditions to give a single bromo product.

In bromine water, multiple bromination occurs, forming 2,4,6-tribromophenol (a white ppt)

NCERT Class 12 Chemistry bromine water reaction with phenol yielding 2,4,6-tribromophenol as a white precipitate.

Note that, unlike benzene, phenol does not require a Lewis acid catalyst for bromination. The electron-donating –OH group activates the aromatic ring sufficiently to polarise Br2 molecules and generate an electrophile, enabling the reaction without the need for a catalyst.

Kolbe’s Reaction:

When phenol is treated with sodium hydroxide, it forms the phenoxide ion, which is even more reactive than phenol in electrophilic aromatic substitution. This increased reactivity allows it to react with carbon dioxide – a relatively weak electrophile – resulting in the formation of ortho-hydroxybenzoic acid as the major product.

NCERT Class 12 Chemistry Kolbe’s reaction showing CO2 electrophilic substitution on sodium phenoxide to give salicylic acid.

Reimer-Tiemann Reaction:

When phenol is treated with chloroform (CHCl3) in the presence of sodium hydroxide, a -CHO group is introduced at the 2 (ortho) position of the aromatic ring. This reaction is called the Reimer–Tiemann reaction.

The reaction proceeds via the formation of a substituted benzal chloride intermediate, which is then hydrolysed under alkaline conditions to yield salicylaldehyde (2-hydroxybenzaldehyde) as the final product.

NCERT Class 12 Chemistry Reimer–Tiemann formylation of phenol with CHCl3/NaOH to give salicylaldehyde at the ortho position.

Reaction with Zn Dust:

When phenol is reacted with zinc dust, benzene is formed.

NCERT Class 12 Chemistry reduction of phenol with zinc dust to benzene.

Oxidation:

When phenol is oxidised with chromic acid, it forms a conjugated diketone called benzoquinone.

Phenols also undergo slow oxidation when exposed to air, producing dark-coloured mixtures that contain quinone derivatives.

NCERT Class 12 Chemistry oxidation of phenol to benzoquinone using chromic acid and slow air oxidation to quinones.

Phenol + Na2Cr2O7/H2SO4 → Benzoquinone (diketone)
Air oxidation → dark-colored quinones

Summary