SCH 4U
Name: _______________________
Unit: Organic Chemistry
Date: _______________________
An Introduction to Alcohols
The simplest way to think of alcohols is as a carbon chain attached to one of the spots on a water
molecule where a hydrogen atom is usually located.
A hydrogen atom will be removed from water so the –OH, now called a hydroxyl group, can attach to a
carbon chain. Usually this occurs across a double or a triple bond and so is classified as an addition
reaction. This type of addition reaction is further classified as hydration because it involves the addition of
a water molecule.
Note that the hydroxyl group is a hydrogen atom covalently bonded to an oxygen atom which is then
covalently bonded to a carbon chain. The hydroxyl group is thus entirely different from the polyatomic ion,
the hydroxide ion, which carries with it a net negative charge and forms ionic bonds with positively
charged ions…like this…
Ionic bond
[Na]1+ [OH]1-
This is the hydroxide ion. It is a polyatomic ion with a net charge and forms
ionic compounds.
The addition of the OH group (the hydroxyl group) will drastically change the properties of the related
hydrocarbon. This is because the O-H bond is so polar. The O-H bond will allow for hydrogen bonding to
occur between neighboring alcohol molecules and between alcohol molecules and water so the boiling
point of an alcohol is much higher than that of the corresponding hydrocarbon and the alcohol is also
much more water soluble.
Example:
ethane (hydrocarbon)
ethanol (alcohol)
δ+
δHydrogen bonding in
addition to London forces
δ+
Only weak London forces between neighboring
molecules.
δ-
Non-polar molecule
Boiling temperature – 89oC
Insoluble in water
Polar molecule
Boiling temperature +78oC
Very soluble in water
Nomenclature of Alcohols
In the IUPAC naming system, the OH functional group adds the suffix –ol to the ending of the typical
chain.
The parent alkane is the longest chain that contains that OH group.
Example:
CH3OH
methanol
this is a highly toxic alcohol that leads
to blindness and often death
CH3CH2OH
ethanol
used in alcoholic beverages, lacquers,
varnishes and perfumes
CH3CH2CH2OH
1-propanol
or propan-1-ol
CH3CH(OH)CH3
2-propanol
or propan-2-ol
solvent for lacquers and waxes and in
brake fluid
common name is isopropanol; sold as rubbing
alcohol; used in the manufacture of gums,
oils and acetone
More than one naming system is in current use for alcohols. Use the method that makes the most sense
to you.
OH
Newer system
Older name, still in use.
Your book uses it.
Classification of Alcohols
1. Primary, Secondary and Tertiary Alcohols
Alcohols are categorized based on the type of carbon that they are attached to. Since carbon atoms have
4 bonds, the atom that has the OH can be attached to 1,2 or 3 carbon atoms as well. This creates primary,
secondary and tertiary alcohols respectively. The classification is important for the types of reactions that
each will undergo because the products are determined by the availability of H atoms in key positions.
Examples:
3- methylbutan-1-ol is a primary
(1o) alcohol
The carbon attached to the
hydroxyl group is attached to
only one other carbon.
Pentan-2-ol is a secondary (2o)
alcohol
2-methylbutan-2-ol is a tertiary (3o) alcohol
You draw the structural formula here…
The carbon attached to the hydroxyl
group is attached to two other
carbons.
2) Polyalcohols
Alcohols that contain more than one OH group are considered to be diols or triols. Antifreeeze for
example is ethane-1.2-diol (or 1,2-ethanediol), more commonly known as ethylene glycol. A common
triol is propane-1,2,3-triol (or 1,2,3-propanetriol) which is known as glycerol. Glycerol is non-toxic. It is a
common ingredient in skin moisturizers, lipsticks and chocolate.
glycerol
3) Cyclic alcohols
These are less common, but the naming procedure is consistent with our system to this point. The
following are some examples:
OH
OH
Cyclohexanol
OH
OH
phenol
1,2-dihydroxybenzene
Practice
1) Write IUPAC names for the following molecules. It might be an idea to draw out a structural formula for
each one before trying to name it.
a)
CH3CH(OH)CH2CH3
b)
CH3CH(OH)CH2CH2CH2(OH)
c)
C6H5(OH)2
2) Draw a structural formula for each of the following:
a)
3-methylbutan-1-ol (could be called 3-methyl – 1 – butanol)
b)
propane-1,2 – diol (could be called 1, 2 – propanediol)
c)
propane-1,3-diol (could be called 1, 3 – propanediol)
d)
pentane – 1, 3, 4 – triol (could be called 1,3,4-pentanetriol)
e)
cyclopentanol
f)
2-methylphenol
g)
2-methylcyclohexanol
h)
all the structural isomers of C5H11OH
3) Decide whether each of the following compounds is a primary, a secondary or a tertiary alcohol.
b)
a)
c)
d)
3) Answer #2 on page 27 of the textbook.
4) Write out a balanced chemical equation to show the production of the most common alcohol product
from the addition reaction between pent-2-ene and water. Use structural formulas in your balanced
chemical equation. Name the product of the reaction. (Remember to use Markovnikov’s Rule, page
26.)