Properties of Alcohols

Alcohols: Contain hydroxyl group. Simplest alcohol is methanol- CH3OH and it’s used as fuel,
chemical feedstocks and solvents. Next in alcohol homologous series is ethanol and used in
alcoholic drinks, fuel and solvent.
• If make methanol using carbon monoxide it’s good because- CO is toxic and increases atom
economy of process.
• Comparing with Alkanes: When comparing alcohol with alkanes, alcohols are less volatile, have
higher melting points and greater water solubility.
• Polarity: Alkanes have non polar bonds because electronegativity of hydrogen and carbon are
similar so only have London Forces. Alcohols have polar O-H bond due to difference in
electronegativity of oxygen and hydrogen atoms. Oxygen more electronegative so delta minus.
• Volatility and Boiling Points: Compounds with low boiling points are volatile so easily to gas.
– Alkanes have London forces only whereas alcohols have hydrogen bonds and London forces.
– The hydrogen bonds between liquid alcohol molecules are stronger.
– They require more energy than overcoming the weaker London Forces in alkanes, to boil.
– So alcohols have lower volatility than alkanes.
• More OH groups means stronger (and more) hydrogen bonds between molecules of alcohol and
greater solubility.
• Solubility in Water: Alcohols are soluble as have OH groups so hydrogen bonds form between the
OH group and water molecules.
• Chain Length: As length of carbon chain increases, the influence of –OH group becomes smaller
so the solubility of longer- chain alcohols becomes more like hydrocarbons- solubility decreases.
• Primary Alcohols: The –OH group is attached to a carbon atom that is attached two hydrogen
atoms and one alkyl/ carbon group. 1o
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• Secondary Alcohols: The –OH group is attached to a carbon atom that is attached to one hydrogen
atom and two alkyl/ carbon groups. In the middle.

Tertiary Alcohols: The –OH group is attached to a carbon atom that is attached to no hydrogen
atoms and three alkyl groups (attached carbon or oxygen). Usually the + shape in skeletal is
tertiary.
• H below is tertiary and D is a secondary.
• Like dissolves like, non- polar dissolves with non- polar, ionic/ polar dissolves with another ionic/
polar