Alcohols
The An organic compound containing a hydroxyl group, -OH. The 'alcohol' in alcoholic drinks is ethanol, produced by the fermentation of sugars and found in wines, spirits and beers. form a A 'family' of organic compounds that have the same functional group and similar chemical properties. . Like all homologous series, the alcohols:
- have the same An algebraic formula that sets out a rule or trend which is followed by all members of a homologous series. For example, all non-cyclic alkanes have the general formula CnH2n+2.
- differ by CH2 in Chemical formula showing the actual number of atoms of each element in a molecule. from neighbouring A substance formed by the chemical union of two or more elements.
- show a gradual variation in A description of the appearance of a substance or how it acts without involving chemical reactions. For example, state, melting point, conductivity, etc., such as their The temperature at which a substance rapidly changes from a liquid to a gas.
- have similar A description of how a substance reacts with other substances. For example, flammability, pH, reaction with acid, etc.
Functional group
The An atom, or group of atoms, that determines the main chemical properties of an organic compound. in the alcohols is the The functional group present in all alcohols, -OH. group, –OH. It is responsible for the typical reactions of alcohols. Take care not to confuse the –OH group with the hydroxide ion, OH–.
General formula
The general formula for the alcohols is CnH2n+1OH (where n is the number of carbon atoms in the molecule).
Worked example
Decanol is an alcohol. Its A collection of two or more atoms held together by chemical bonds. contain 10 carbon The smallest part of an element that can exist.. Predict the molecular formula of decanol and explain your answer.
The formula will be C10H21OH. This is because n = 10. So, 2n + 1 = (2 Ă— 10) + 1 = 20 + 1 = 21.
Question
Hexanol is an alcohol. Its molecules contain 6 carbon atoms. Predict the molecular formula of hexanol.
The formula will be C6H13OH.
Structures
The table shows four alcohols, their molecular formulae, their structural formulae and their displayed formulae.
Question
Draw the displayed formula of pentanol, C5H11OH. Show all the covalent bonds.
Reactions of alcohols
The alcohols undergo Burning in a plentiful supply of oxygen or air. Complete combustion of a hydrocarbon produces water vapour and carbon dioxide. to form carbon dioxide and water. For example, ethanol is used as a fuel:
ethanol + oxygen → carbon dioxide + water
C2H5OH + 3O2 → 2CO2 + 3H2O
However, the alcohols can also be Chemical substances are oxidised by the addition of oxygen, removal of hydrogen or the removal of electrons. without The process of burning by heat. to produce A homologous series of compounds that contain the carboxyl functional group, -COOH.. For example, ethanol can be oxidised to ethanoic acid using an A substance that can oxidise other substances in chemical reactions.. It is easier to understand what happens if ethanol is shown as CH3CH2OH in the balanced equation:
ethanol + oxidising agent → ethanoic acid + water
CH3CH2OH + 2[O] → CH3COOH + H2O
Notice that the left-hand side of the ethanol molecule is unchanged. The reaction involves the –OH group on the right-hand side.
Question
Propanol is oxidised by using an oxidising agent. Name the carboxylic acid formed in the reaction.
Propanoic acid.