Alcohols

What is here?

Alcohols are organic compounds that:

  • contain the hydroxyl functional group, —OH
  • have molecules based on alkanes in which one of the H atoms is replaced by an —OH group
  • form a homologous series which has the general formula CnH2n+1OH.

Use your mouse (or finger on touch devices) to move or scale molecules. Double tap to stop and start each animation.

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ball and stick model
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methanol, CH3OH

ethanol, C2H5OH

propan-1-ol, C3H7OH

propan-2-ol, C3H7OH

Homologous series

A homologous series is a series of compounds which:

  • have the same functional group
  • have the same general formula
  • differ by CH2 in molecular formulae from neighbouring compounds
  • show a gradual variation in physical properties, such as their boiling points
  • have similar chemical properties.

Functional groups

A functional group is an atom, group of atoms or a bond responsible for the characteristic chemical reactions of a substance. The functional group in alcohols is most easily shown as —OH.

A general formula is a chemical formula used to represent the members of a homologous series. The general formula for the alcohols is CnH2n+1OH

Hexanol molecules, for example, contain six carbon atoms:

n = 6
2n + 1 = (2 × 6) + 1 = 13

So the molecular formula for hexanol is C6H13OH.

Structural and displayed formulae

A structural formula shows the number of atoms of each element in a molecule, and their positions in the molecule.

A displayed formula shows the same information as a structural formula, but in addition it shows the bonds between the atoms.

Name of alcoholStructural formulaDisplayed formula
methanolCH3OH
ethanolCH3CH2OH
propan-1-olCH3CH2CH2OH
propan-2-olCH3CH(OH)CH3

Isomers of butanol

Isomers are substances that have the same molecular formula, but a different arrangement of atoms:

  • propan-1-ol and propan-2-ol are position isomers in which the hydroxyl group is found in different positions on the carbon chain.

The molecular formula of butanol is C4H9OH. Butanol has four isomers:

  • butan-1-ol and butan-2-ol
  • 2-methylpropan-1-ol and 2-methylpropan-2-ol.

The molecular models here show these four isomers. Two of them have branched carbon chains.

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butan-1-ol

butan-2-ol

2-methylpropan-1-ol

2-methylpropan-2-ol