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Do you know that over 100 billion litres of ethanol is produced every year globally, or the first antiseptic used in surgery was Phenol? All these interesting facts are discussed in Alcohols, Phenols, and Ethers which are important classes of compounds that feature oxygen-containing organic compounds. When the OH group replaces the hydrogen atom in aliphatic hydrocarbons, Alcohols are formed same goes for phenols when the OH group replaces the hydrogen of aromatic hydrocarbons, then Phenols are formed while Ethers are formed when the alkoxy (R-O) or aryloxy (Ar-O) group substitutes the hydrogen atom in hydrocarbons.
NCERT Class 12 Chemistry notes of Chapter 7 provide a structured approach to understanding the classification, properties, preparation, and reactions. NCERT Notes are prepared by our subject experts in a comprehensive way that helps students understand the concepts in a very simple and easy way. These notes cover all the topics as prescribed by the latest CBSE syllabus, and selected previous year questions are also added to help enhance the clarity and problem-solving ability of students.
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These concise NCERT notes cover all the key concepts of alcohol, phenol and ethers to help students in quick revision before the exam. You can download the NCERT notes PDF from the button given below
Alcohols, Phenols and Ethers notes are given below and they covers all concepts of the NCERT textbook and explains them in a concise and easy-to-understand manner. Whether revising or studying for the first time these NCERT notes are a boon for students who aim to score well in their exams.
The classification of compounds Alcohold, Phenols and Ethers makes their study systematic and hence simpler.
1. Alcohols Mono, Di, Tri or Polyhydric alcohols
Alcohols and phenols are classed as monohydric, dihydric, trihydric, or polyhydric depending on how many hydroxyl groups they have in their molecules.
According to the hybirdisation of Carbon atom to which the hydroxyl group is attached, Monohydric alcohols are further classified:
(i). Compounds containing
They are further classified as:
(a). Primary, secondary and tertiary alcohols: The –OH group is attached to primary, secondary and tertiary carbon atom.
Primary alcohol
Secondary alcohol
Tertiary alcohol
Primary Secondary Tertiary
(b). Allylic alcohols: The OH group is attached to a sp3 hybridised carbon adjacent to the carbon-carbon double bond, that is to an allylic carbon.
(c). Benzylic alcohols: The OH group is attached to a sp3 hybridised carbon atom next to an aromatic ring.
(ii) Compounds containing
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:
2. Phenols Mono, Di and trihydric phenols
3. Ethers
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.
1. 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.
IUPAC Nomenclature:
Number the carbon so that the OH group gets the lowest possible position
Remove e from the alkane name and add ol.
Mention the position of the OH group
2. Phenols
The simplest hydroxy derivative of benzene is phenol. It is its common name and also an accepted IUPAC name.
IUPAC Nomenclature
3. 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.
IUPAC Nomenclature
Alcohols have sp3 hybridized oxygen atoms and hybrid atomic orbitals in a tetrahedral configuration. The R group determines the value of the ROH bond angle. Due to lone pair repulsion, this angle for methyl alcohol is (C – O – H) 108.9°.The -OH group in phenols is connected to sp2 hybridized carbon, giving the C – O bond a partial double bond nature.
Alcohols are prepared by the following methods:
(i). By acid catalysed hydration
This reaction is in accordance with Markonikov's rule,
CH3CH=CH2 + H2O → CH3-CH(OH) - CH3
Mechanism
It involves 3 steps:
Step1. Protonation of alkene to form carbocation by electrophilic attack of H3O+
Step 2. Nucleophilic attack of water on carbocation
Step 3: Deprotonation to form an alcohol
(ii). By hydroboration-oxidation
By hydroboration-oxidation of alkenes, alcohols can be prepared, where BH3 adds across the double bond followed by oxidation with H2O2/NaOH to give alcohols with anti-Markovnikov orientation.
(i). By reduction of aldehydes and ketones
RCHO + H2 → RCH2OH
(ii). By reduction of carboxylic acids
All three types of monohydric alcohols can be prepared by the use of Grignard reagents. Grignard reagents form addition compounds by nucleophile attack with aldehydes and ketones which on hydrolysis with dilute acid yields alcohol.
Phenol, also known as carbolic acid, and is commercially produced synthetically. In the laboratory, phenols are prepared from benzene derivatives by any of the following methods:
Chlorobenzene is fused with NaOH at 623K and 320 atmospheric pressure. Phenol is obtained by acidification of sodium phenoxide so produced. The reaction occurs as follows.
Benzene is sulphonated with oleum and benzene sulphonic acid so formed is converted to sodium phenoxide on heating with molten sodium hydroxide. Acidification of the sodium salt gives phenol. The reaction occurs as follows:
A diazonium salt is formed by treating an aromatic primary amine with nitrous acid (NaNO2 + HCl) at 273-278 K. Diazonium salts are hydrolysed to phenols by warming with water or by treating with dilute acids. The reaction occurs as follows.
Phenol is manufactured from the hydrocarbon, cumene. Cumene (isopropylbenzene) is oxidised in the presence of air to cumene hydroperoxide. It is converted to phenol and acetone by treating it with dilute acid. Acetone, a by-product of this reaction, is also obtained in large quantities by this method. The reaction occurs as follows:
Alcohols and phenols consist of two parts, an alkyl/aryl group and a hydroxyl group. The properties of alcohols and phenols are chiefly due to the hydroxyl group. The nature of alkyl and aryl groups simply modify these properties:
(i). Boiling points of alcohols and phenols rise with increasing carbon atoms due to stronger van der Waals forces, but decrease with branching due to reduced surface area. They have higher boiling points than hydrocarbons, ethers, haloalkanes, and haloarenes of similar masses, mainly because of intermolecular hydrogen bonding. For example, despite similar molecular masses, ethanol boils much higher than propane, while methoxymethane shows an intermediate boiling point, reflecting the absence of hydrogen bonding in ethers.
(ii). Lower alcohols are colourless liquids, C5–C11 alcohols are oily liquids, and C12 and higher alcohols are waxy solids. Alcohols are miscible with water because their hydroxyl groups can form H-bonds with water. With increasing molecular mass, solubility decreases. Because polar molecules have intermolecular hydrogen bonding, the boiling points of alkanes are greater than expected.
(iii). These are colourless liquids or crystalline solids that turn coloured over time due to gradual oxidation in the presence of air. Carboxylic acid is another name for phenol. Phenols establish intermolecular H-bonds with other phenol molecules and with water due to the presence of a polar -OH bond.
(iv). Alcohols and phenols are soluble in water due to hydrogen bonding with water molecules. However, solubility decreases as the size of the hydrophobic alkyl or aryl group increases. Lower molecular mass alcohols are completely miscible with water.
Alcohols react both as nucleophiles and electrophiles. The bond between O–H is broken when alcohols react as nucleophiles. They are versatile compounds.
Alcohols as Nucleophiles
Alcohols as electrophiles
Reactions involving cleavage of the O–H bond in alcohols and phenols typically involve the release of a proton, showcasing their acidic nature. These reactions often form alkoxides or phenoxides when treated with active metals or strong bases.
i). Acidity of alcohols and phenols
a). Reaction with metals
b). Acidity of alcohols
The acidic character of alcohols arises from the polar O–H bond. Electron-releasing groups increase electron density on the oxygen atom, reducing the O–H bond polarity and thus decreasing the acidity.
Alcohols are weaker acids than water.
b). Acidity of phenols
Because the phenoxide ion is stabilized through resonance, phenol is more acidic than alcohols. The presence of an electron withdrawing group raises phenol's acidity by stabilizing the phenoxide ion, whereas the presence of an electron releasing group lowers phenol's acidity by destabilizing the phenoxide ion.
(ii). Esterification
Reaction of Alcohols and phenols with carboxylic acids, acid chlorides and acid anhydrides form esters.
Ar/R-OH + (RCO,)2O + H+↔ Ar/ROCOR, + RCOOH
R/ArOH + R,COCl Pyridine→ R/ArOCOR, + HCl
Reactions involving cleavage of the C–O bond in alcohols typically occur during substitution or elimination, where the hydroxyl group is replaced or removed forming alkyl halides or alkenes.
i). Reaction with hydrogen halides
ROH + HX yields→ RX + H2O
ii). Reaction with phosphorus trihalides:
iii). Dehydration
Alcohols undergo dehydration means removal of a molecule of water to form alkenes on treating with a protic acid.
Order of reaction
Tertiary > Secondary > Primary
Mechanism of dehydration
Step 1: Formation of protonated alcohol
Step 2: Formation of carbocation
Step 3: Formation of ethene by elimination of a proton.
iv). Oxidation
Formation of a carbon oxygen double bond with cleavage of an O-H and C-H bonds is involved in oxidation of alcohol.
Alcohol, Acidified KMnO4→ Carboxylic acid
RCH2OH Oxidation→ RCHO yields→ RCOOH
Phenol undergoes characteristic reactions. Its aromatic ring is highly reactive due to the activating effect of the –OH group.
i). Electrophilic aromatic substitution
Electrophilic substitution reactions take place on aromatic ring in phenols. The OH group attached to the benzene ring activates it towards electrophilic substitution. Also, it directs the incoming group to ortho and para positions in the ring as these positions become electron rich due to the resonance effect caused by OH group.
a). Halogenation
Anisole reacts with an alkyl halide and acyl halide introducing alkyl and acyl groups in ortho and para positions.
b). Nitration
With dilute nitric acid at low temperature (298 K), phenol yields a mixture of ortho and para nitrophenols. The reaction occurs as follows.
ii). Reimer-Tiemann reaction
Phenols for aromatic compounds containing EDG when refluxed with CHCl3 and alkali yield o- and p- hydroxybenzaldehyde. The ortho product is the predominant product. It is an electrophilic substitution on PhO- ion. The electrophile is dichlorocarbene (:CCl2) which contains a C with only six electrons.
iii). Kolbe’s reaction
Phenol when heated at(390-410K) under pressure with CO2 and alkali gives salicylic acid after acidification in addition to some amount of p-isomer.
iv). Reaction of phenol with zinc dust
When phenol is distilled with zinc dust, benzene is obtained. The reaction occurs as follows:
v). Oxidation
Two commercially important alchols are Methanol and ethanol.
Methanol (CH3OH)
Wood-spirit is another name for it. It is a clear liquid with no discernible colour. It reaches a temperature of 337 degrees Fahrenheit when it boils. It is extremely poisonous. Even little doses can cause blindness, and excessive doses can be very fatal.
Paints, varnishes, and other products use it as a solvent.It can be used to make formaldehyde.
Ethanol (C2H5OH)
It is known as denatured spirit when combined with CuSO4 and pyridine.It is a colourless liquid having boiling point 351 K.
It is a good solvent, Sterilization of surgical tools in laboratories and hospitals.
Ethers are organic compounds in which two alkyl or aryl groups are bonded to the same oxygen atom.
1). By dehydration of alcohols
Alcohols lose water in the presence of protic acids like H2SO4 or H2PO4. The product formed alkene or ether depends on temperature. For instance, ethanol gives ethene at 443 K, while at 413 K, it mainly forms ethoxyethane.
CH3CH2OH
CH3CH2OH
2). Williamson synthesis
It is the best method to prepare all type of ethers, that is, simple, mixed or aromatic ethers. Here, alkyl halides are treated with sodium alkoxide in presence of magnesium to give ethers. It involves SN2 mechanism during the attack of R-O- on R-X, that is, backside attack occurs here. The reaction occurs as follows:
Some examples include:
Since ethers' C-O bonds are polar, they have a net dipole moment. Their boiling points are equivalent to alkanes with similar molecular weights, although they are lower than alcohols. It's because ethers don't have H-bonding. Ether miscibility with water is similar to that of alcohols of same molar mass. It's because ethers, like alcohols, can make H-bonds with water.
Ethers are generally unreactive but undergo cleavage with strong acids like HI or HBr, forming alcohols and alkyl halides.
The cleavage of C-O bond in ethers takes place under drastic conditions with excess of hydrogen halides. The reaction of dialkyl ether gives two alkyl halide molecules
R-O-R + HX → RX + R-OH
R-OH + HX → R-X + H2O
The alkoxy group is ortho, para directing and activates the aromatic ring towards electrophilic substitution in the same way as in phenol.
i). Halogenation
ii). Friedel craft’s reaction
Anisole reacts with an alkyl halide and acyl halide introducing alkyl and acyl groups in ortho and para positions.
iii). Nitration
Anisole reacts with a mixture of concentrated sulphuric and nitric acids to yield a mixture of ortho and para nitroanisole. The reaction occurs as follows.
Slected questions from previous year exams are given below:
Question 1: Which of the following are benzylic alcohols?
(1) (i) and (ii)
(2) (iii) and (iv)
(3) (ii) and (iii)
(4) (ii) and (iv)
Answer:
The answer is the option (ii) and (iii).
The most prominent way to identify benzylic alcohol is to check if an -OH group is attached to a
As in the case of option (ii) and (iii), the
Hence, the answer is the option (3).
Question: Phenol can be distinguished from ethanol by the reactions with _________.
(i)
(ii)
(iii) Neutral
(iv) All the above
(1) (i) and (iii)
(2) (iii) and (iv)
(3) (ii) and (iii)
(4) None of above
Answer:
The answer is the option (i) and (iii).
Phenol can easily be distinguished from ethanol by adding bromine water as it results in a white ppt of tri-bromo phenol or Neutral FeCl3 can also be used for this purpose. But ethanol being aliphatic alcohol will not react with either of the compounds.
Hence, the answer is the option (1). Question:
Question: Which of the following reactions will yield phenol?
(1) (A), (B) and (C)
(2) (A), (B) and (D)
(3) (A), (C) and (D)
(4) (B), (C) and (D)
Answer:
The answer is the option (A), (B), (C). To carry out these reactions, the conditions required should be easy to maintain. The reaction occurring in (D) is a nucleophilic substitution of chlorobenzene which is not feasible as it requires drastic temperature and pressure conditions.
The reaction given in (A) is the Dow process, (B) is aniline diazotisation and (C) option contains a reaction from benzene sulphonic acid. All these reactions are feasible due to manageable reaction conditions.
Hence, the answer is the option (1).
The link of the NCERT Class 12 chemistry chapter-wise notes is given below:
Subject-wise links of ncert solutions are given below:
Subject-wise links of ncert exemplar solutions are given below:
NCERT Books and Syllabus
The links below will give you access to books and a syllabus for Class 12
Alcohols are organic compounds that contain one or more hydroxyl groups attached to a carbon atom. They are classified based on the number of carbon atoms connected to the -OH bearing carbon:
primary (1°), secondary (2°), or tertiary (3°) alcohols.
Both alcohols and phenols contain hydroxyl groups, the key difference lies in the structure. Alcohols have the -OH group attached to an aliphatic carbon atom , whereas phenols have the -OH group attached to a carbon in an aromatic ring.
Alcohols have diverse applications, including as solvents, in the production of pharmaceuticals, and as fuels. Ethanol is used in alcoholic beverages, as an industrial solvent, and as a biofuel.
Alcohols can undergo several key reactions, including dehydration to form alkenes, oxidation to produce aldehydes or ketones, and esterification where alcohol reacts with acids to form esters.
Ethers are generally less reactive due to the stable nature of the C-O-C bond. They do not readily participate in reactions like alcohols and phenols because they lack a hydroxyl group, which is reactive and can donate protons.
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