5. Introduction to alcohol
Alcohol is both a beverage providing some sustenance and a drug. For thousands
of years, alcohol has been consumed in a medicinal, celebratory, and ritualistic
manner. It is drunk in just about every country and often in excessive amounts.
Alcohol can be made from a variety of different starch foods through the processes
The alcohols form a homologous series. Like all homologous series, the alcohols.
Alcohol is a psychoactive drug. A psychoactive drug is any
substance that crosses the blood-brain barrier primarily affecting the
functioning of the brain, be it altering mood, thinking, memory, motor
control, or behavior.
7. Functional group of alcohol
• Alcohol molecules all contain the hydroxyl (-OH) functional group.
They are a homologous series and have the general formula
CnH2n+1OH. Their names all end in -ol.
8. The rules for naming an alcohol are
1. Find the longest carbon chain and name it.
2. Number the carbon atoms in the chain so that the functional group
(in this case, the hydroxyl group) has the lowest possible number.
3. Identify any branches joined onto the main chain and name them.
4. Identify each branch by a number indicating its position. If more
than one branch is present then a prefix must be used.
10. TYPES OF ALCOHOLS
1. Monohydric alcohols are organic compounds containing one
hydroxyl group and are formulated as CnH2n+1OH.
2. Dihydric alcohols contain two hydroxyl groups per molecule and
they are named as glycols
3. Trihydric alcohols contain three hydroxyl groups per molecule and
they are named as triols
11. Nomenclature of Alcohols
Alcohols with one to four carbon atoms are frequently called by
common names, in which the name of the alkyl group is followed by the
13. Rules for naming the alcohols
1.Find the longest chain containing the hydroxy group (OH). If there is
a chain with more carbons than the one containing the OH group it will
be named as a subsitutent.
2.Place the OH on the lowest possible number for the chain. With the
exception of carbonyl groups such as ketones and aldehydes, the alcohol
or hydroxy groups have first priority for naming.
3.When naming a cyclic structure, the -OH is assumed to be on the first
carbon unless the carbonyl group is present, in which case the later will
get priority at the first carbon.
4.When multiple -OH groups are on the cyclic structure, number the
carbons on which the -OH groups reside.
15. Physical properties
• The physical properties of alcohol can be explained by the following
• Alcohols are colourless.
• They generally give a sweet smell except for glycerol and a few lower
• They are flammable and produce a blue flame.
• They don’t produce any smoke while burning.
• They are generally liquid at room temperature. Although glycerol is a
1. Boiling of alcohol : Alcohols generally have higher points in
comparison to other hydrocarbons having equal molecular masses.
2. Solubility of alcohol : The solubility of alcohol in watter is governed
by the hydroxyl group present.
3. Acidity of alcohol : alcahol react with active metals such as
Sodium,potassium etc. To form the corresponding alkoxide, these
reactions of alcohols indicate their acidic nature.
The acidic nature of alcohol is due to the polarity of –OH bond.
18. Chemical properties
The chemical properties of alcohol can be explained by the following
1. Oxidation Reaction of Alcohol – Alcohols produce aldehydes and
ketones on oxidation. The reaction is given below .
C₂H₅OH + 2O 🡪 CH₃COOH + H₂O
Ethanol Methanoic acid
2. Combustion of Alcohol – On heating ethanol gives carbon dioxide
and water and burns with a blue flame. The reaction is given below .
C₂H₅OH + 3O₂ 🡪 2CO₂ + 3H₂O
3. Dehydration of Alcohol – Alcohol can be dehydrated in an acidic
medium. The removal of water molecules from a compound is called
dehydration. Upon dehydration of alcohol alkenes are produced. The
reaction is given below .
C2H5OH (conc. H₂SO₄,▵)→C₂H₄ + H₂O