Download Alcohols

unlimited number of carbon compounds can
be formed by the addition of a functional
group to a hydrocarbon.
A functional group is a reactive portion of a
molecule. The combinations of functional
groups with hydrocarbons produce a vast
number of compounds.
Organic molecules containing a hydroxyl group
are known as alcohols.
Classification of Alcohols
Alcohols are classified as primary, secondary,
and tertiary
Classification is determined by the number of
alkyl group to the carbon bonded to the
hydroxyl.
 Primary alcohols
In a primary (1°) alcohol, the carbon which carries
the -OH group is only attached to one alkyl group.
Notice that it doesn't matter how complicated the attached
alkyl group is. In each case there is only one linkage to an
alkyl group from the CH2 group holding the -OH group.
Secondary alcohols
In a secondary (2°) alcohol, the carbon with
the -OH group attached is joined directly to
two alkyl groups, which may be the same or
different.
Tertiary alcohols
In a tertiary (3°) alcohol, the carbon atom
holding the -OH group is attached directly to
three alkyl groups, which may be any
combination of same or different.
In phenols the -OH group is directly attached
to a carbon that is part of an aromatic ring.
Alcohols and phenols are similar in some
ways, but there are enough differences so that
they are considered different functional
groups.
One major difference is that phenols are
typically about a million times more acidic
than alcohols.
Physical Properties
Boiling Points
The chart shows the boiling points of some
simple primary alcohols with up to 4 carbon
atoms.
They are:
They are compared with the equivalent alkane
(methane to butane) with the same number
of carbon atoms.
Notice that:
• The boiling point of an alcohol is always much
higher than that of the alkane with the same
number of carbon atoms.
• The boiling points of the alcohols increase as
the number of carbon atoms increases.
• The patterns in boiling point reflect the
patterns in intermolecular attractions.
 Hydrogen bonding
• Hydrogen bonding occurs between molecules
where you have a hydrogen atom attached to
one of the very electronegative elements fluorine, oxygen or nitrogen.
• In the case of alcohols, there are hydrogen
bonds set up between the slightly positive
hydrogen atoms and lone pairs on oxygens in
other molecules.
• The hydrogen atoms are slightly positive
because the bonding electrons are pulled
away from them towards the very
electronegative oxygen atoms.
Solubility of alcohols in water
• The small alcohols are completely soluble in
water.
• Solubility falls as the length of the
hydrocarbon chain in the alcohol increases.
Chemical Properties
1. Ceric ammonium nitrate test
• General test for alcohols
• +ve result  red coloration indicates the
presence of alcohols.
2. Oxidation Reaction
• This test is to distinguish Primary and
secondary alcohols from tertiary alcohols
• Primary alcohols can be oxidised to either
aldehydes or carboxylic acids depending on
the reaction conditions.
Step 1
aldehyde
Step 2
carboxylic acid
• Secondary alcohols are oxidised to ketones
• Tertiary alcohols does not react because there
is no free H to loss
• +ve result: Purple  colorless
3. Ferric Chloride test:
• Addition of aqueous FeCl3 to phenol gives a
colored solution.
• Depending on the structure of phenol, the
color can vary from green to purple.
Cl
Fe
Cl
O
OH
+
Light yellow
FeCl3
+
Violet
HCl
4. Solubility with NaOH (acidity test)
• Phenol is a weak acid therefore reacts with a
base
• Alcohols are less acidic than Phenols therefore
are not neutralized by NaOH
O-Na+
OH
+
NaOH
+
H2O