Download 10.3 Alcohols

10.3 Alcohols
• These compounds have an -OH attached to
the carbon chain.
• This functional group is called a hydroxyl
group.
• Note: The oxygen is bonded to the carbon in
a covalent bond.
• The hydrogen is then bonded in a covalent
bond to the oxygen, it is not a hydroxide ion
that is attached to the carbon atom.
Classes of Alcohols
• The number of R groups attached to the
carbon with the hydroxyl group is used to
classify alcohols as primary, secondary or
tertiary alcohols:
• Primary alcohol, where only one R group is
attached to the carbon to which the hydroxyl
group is attached:
R - CH2 - OH
• Secondary alcohol, where two R groups are
attached to the carbon to which the hydroxyl
group is attached:
R1
I
R2 - CH - OH
• Tertiary alcohol, where three R groups are
attached to the carbon to which the hydroxyl
group is attached:
R1
I
R2 - C – OH
I
R3
Naming Alcohols
• Determine the parent alkane as the
longest continuous chain that includes
the carbon attached to the -OH group.
• Number the carbons in this chain so
that the carbon attached to the -OH
group has the lowest number.
• Drop the -e ending from the name of
the parent alkane and replace it with –ol
• Alcohols containing two or three -OH
groups are called diols and triols.
Common Names of Alcohols
• Many alcohols have common names based on
naming the hydrocarbon chain as an alkyl group
and adding the word alcohol.
• For example:
• IUPAC name: Common name:
formula:
methanol
methyl alcohol
ethanol
ethyl alcohol
propan-1-ol
1-propyl alcohol
• These are all primary alcohols
Structural
CH3 - OH
CH3 - CH2 - OH
CH3-CH2-CH2 - OH
Example of a diol
ethane-1,2-diol or ethylene glycol
CH2 - CH2
I
I
OH OH
Alcohols with an aromatic ring are called phenols:
CH3
OH
phenol
OH
2-methylphenol
(o-cresol)
Cyclic Alcohols
• C6H11OH(l) is a cyclohexanol.
OH
• The following diagram is for cyclohexaneOH
1,2-diol
OH
Properties of Alcohols
• Intermolecular hydrogen bonding is possible
since the -OH group is slightly polar,
therefore boiling points are quite high and so
even the smallest alcohols are liquids at room
temperature.
• Due to the slight polarity of the -OH group,
small chain alcohols, up to 4C, are soluble in
water but from 5C up alcohols have limited
solubility due to the non-polar nature of the
C chains.
pentan-1-ol
pentan-2-ol
pentan-3-ol
2-methylbutan-1-ol
2-methylbutan-2-ol
3-methylbutan-2-ol
2,2-dimethylpropanol
3-methylbutan-1-ol
Elimination Reactions
• Elimination reactions are essentially the
reverse of the addition reactions we saw
above.
• Halogens or hydroxyl groups are removed or
eliminated from the molecule to produce a
double bond in an alkene.
Elimination
• For example: elimination of a halogen:
H H H
H H H
I I I
I I I
H - C - C - C – H + OH-  H - C = C - C – H + HOH + BrI I I
I
H Br H
H
2-bromopropane
propene
Elimination
• Or: the elimination of water:
H H
I I
H - C - C– H
I I
H OH
ethanol
H H
acid

I I
H-C=C –H
ethene
+ HOH
Elimination
• Elimination reactions are important as they
produce useful unsaturated compounds for
the synthesis of more compounds, particularly
plastics.