Class – 12 Chemistry
Chapter 7 – Alcohols, phenols and Ethers

1. Introduction
   Alcohols are compounds that have a hydroxyl group
   ( – OH)
   attached to a saturated
   carbon atom. Enols are compounds that have a hydroxyl group attached to an
   unsaturated carbon atom of a double bond. The saturated carbon can be alkyl,
   alkenyl, alkynyl, cycloalkyl, or benzyl. If, on the other hand, a hydroxyl group is
   attached to a benzene ring. Phenols are the name given to these compounds.
   The alcohols are further classified as monohydric (containing one

• OH
  group),
  dihydric (containing two
• OH
  groups), and trihydric (containing three
• OH
  groups) (containing three
• OH
  groups).
  Alcohol is used in both industry and everyday life. Chiefly ethanol, for example, is
  a common spirit used to polish wooden furniture. Sugar, cotton, and paper are all
  composed of compounds that contain groups. Phenols are found in a variety of
  important polymers, including Bakelite, as well as pharmaceuticals such as Aspirin.
  Ethers are commonly used as anaesthetics and solvents.
  In alcohols, the oxygen of the group is attached to carbon by a sigma ( bond formed
  by the overlap of a sp hybridised forbital of carbon with a sp hybridised orbital of
  oxygen. The following figure depicts structural aspects of methanol, phenol and methoxymethane.Classification of Alcohols
  Mono, Di, Tri or Polyhydric Compounds
  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:
  1.1 Compounds Containing Csp3 – OH 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
  (a) Primary, secondary and tertiary alcohols:
  In these types of alcohols, the –OH group is
  attached primary secondary and tertiary carbon
  atom, respectively as depicted below.for example:The primary alcohol is 1-propanol, the secondary alcohol is 2-butanol, and the tertiary alcohol is 2-methy-2-propanol.
  (b) Allylic alcohols: In these
  alcohols, the –OH group
  is attached to an sp3
  hybridised carbon next to
  the carbon-carbon double
  bond, i.e. to an allylic
  carbon. For example
  Primary (1⁰
  )
  -CH₂-OH CH-OH -C-OH
  Secondary (2⁰
  ) Tertiary (3⁰
  )
  CH₂ CH-CH₂-OH

(c)Benzylic alcohols: In these alcohols,
the –OH group is attached to an sp3
–hybridized carbon atom next to an
aromatic ring.
For example Allylic and benzylic
alcohols may be primary, secondary
or tertiary

Isomerism Shown by Alcohols
Alcohol may show chain, position and
functional isomerism.
For example,

1. Butan-1-ol and 2-Methylpropan-1-ol are chain
   isomers.
2. Propan-1-ol and Popan-2-ol are position
   isomers.
3. Benzyl alcohol and Anisole are functional
   isomers.

General Methods of Preparation of Alcohols

1. Hydrolysis of Halides
   Alkyl halides when boiled with an aqueous solution of an alkali hydroxide give alcohol through nucleophilic substitution mechanism.

R-X + KOH → R-OH + KX

This general 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.

2. Hydration of Alkenes
   Direct hydration takes place by adding water in the presence of a catalyst.

Preparation of alcohols:

• Key takeaway – Hydration and oxymercuration-demercuration gives Markonikov’s product but
  hydroboration-oxidation gives Anti-markonikov’s product.
• Misconception – Hydroboration follows Markonikov’s rule but in this case, the electron deficient
  species is Boron and not Hydrogen.
• Note – On replacing water with carboxylic acid in hydroboration-oxidation, the product obtained is
  alkane instead of alcohol.
• Note – Tertiary alcohols cannot be obtained by reduction of carbonyl compounds.
• Fact – If we use NaOH as a reductant in reduction of carbonyl compounds to alcohols, the process is
  known as Darzen’s process.
• Tips and tricks – In conversion of oxirane to alcohols using Grignard’s reagent, the alkyl part adds to
  the carbon with less steric hindrance as it proceeds via SN2 mechanism.

1. PHYSICAL PROPERTIES OF ALCOHOLS
   (a) The lower alcohols are liquids while higher having more than 12 carbon atoms are solids. They are colourless,
   neutral substance with characteristic sweet, alcoholic odour and burning taste.
   (b) The lower alcohols are readily soluble in water and the solubility decreases with the increase in molecular
   weight.
   The solubility of alcohols in water can be explained due to the formation
   of hydrogen bond between the highly polarized –OH groups present
   both in alcohols and water.
   However, in higher alcohols, the hydrocarbon character (alkyl chain)
   increases, showing a steric hindrance. Hence, the solubility in water decreases.
   When the ratio of C:OH is more than 4, alcohols have little solubility in water.
   (c) Boiling points of alcohols are much higher than those of the corresponding
   alkanes. It is due to the intermolecular hydrogen bonding present
   between the hydroxyl groups of the two molecules of an alcohol with the
   result several molecules are associated to form a large molecule.
   Among the isomeric alcohols, b.p. and m.p. show the following trend.
   Primary > Secondary > Tertiary
   This is because of the fact that in secondary and tertiary alcohols, the alkyl part (hydrogen character) outweighs
   the –OH group due to branching.
   (d) Lower alcohols form solid addition compounds with anhydrous metallic salts like CaCl2
   and MgCl2
   , viz., CaCl2
   ,
   4C2
   H5
   OH and MgCl2
   .6C2
   H5
   OH
   By analogy to water of crystallization, these alcohols molecules are referred to as alcohols of crystallization.
   For this reason, alcohols cannot be dried over anhydrous calcium chloride. Chemical Properties of Alcohols
   Alcohols give the following type of reactions:
   Reactions with cleavage of O–H bond:
   The acidic nature of alcohols is exhibited by
   these reactions. They do not give H+ in aq. solution
   as they are less acidic than water.
   Reaction with metals:
   Alcohols reacts with alkali metals like Na
   and K for the formation of metal alkoxides which
   further react with haloalkanes to form ethers.for example 2R–OH+2Na by product 2R–ONa+H2. Some Facts about Alcohols
   ●Alcohols show position, chain and functional
   isomerism, For ex. CH3OCH3 and C2H5OH are
   functional isomers.
   ●R–OH + ceric ammonium nitrate Red colour
   ●CH3OH is called wood sprit or carbinol. (60%
   CH3OH).
   ●Ethanol is also known as grain alcohol.
   ●100% ethanol is absolute alcohol.
   ●Power alcohol is 20% ethanol + 80% gasoline.
   It is used as fuel in motor vehicles.
   ●Rectified spirit is 95.47% ethanol + 4.53%
   water.
   ●Isopropyl alcohol is also known as rubbing
   alcohol.
   ●Commercial ethanol is deleberately made
   unfit for human consumption as liquor by
   mixing it with methanol or petrol. (Denatured
   or methylated sprit.)
   ● Tendency of alcohols to form H-bonds:
   primary > secondary > tertiary.
   ●Order of R–OH to form ester with inorganic
   acids follows the order: tertiary > secondary > primary.
   ●A mixture of 95.57% C2H5OH and 4.43% water
   boils at constant temp., i.e., an azeotropic
   mixture.
   Physical properties of ethylene glycol
   ●Ethylene glycol is a clear, sweet, slightly
   viscous liquid.
   ● It is soluble in ethanol and water.
   ● The B.P. of glycol is 470 K.
   ● Ethylene glycol is highly poisonous; animals
   or humans that drink the solution become
   very ill and may die.
   Uses of ethylene glycol
2. In manufacturing dioxane and Dacron.
3. As a solvent and as a preservative.
4. As an anti-freeze in automobile radiators.
5. As an explosive in the form of dinitrate. Physical properties of Glycerol. ●Due to presence of greater extent of H-bonding
   in glycerol, it becomes more viscous than
   other alcohols.
   ●Similarly due to greater extent of hydrogen
   ●Bonding, glycerol has highest boiling point. ● Among alcohols (290°C).
   ●Glycerol is soluble in water and is a colourless. ● oily liquid.
   ●Glycerol is hygroscopic in nature. #Uses of glycerol
   Glycerol finds its application in various field as
   listed below:
   ●It is used as sweetening agent in beverages,
   confectionary & medicines being non-toxic in
   nature.
   ●It is used as lubricant in watches. ●It is used as a preservative
   ●In the preparation of printing inks, non-drying
   inks and stamp pad inks.
   ●In the manufacture of synthetic fibres and
   plastics.
   ●In the preparation of good quality soap,
   vanishing creams, hand lotions, tooth pastes
   and shaving creams. ● Dynamite is a mixture of Kieselguhr and glycerol.