Organic Chemistry

  • Organic Chemistry is the scientific study of the structure, properties, and reactions of organic compounds. Organic compounds are those which contain carbon.
  • For conventional reasons metal carbonates, carbon dioxide and carbon monoxide are not included in organic compounds.
  • Hydrocarbons are the simplest organic compounds and they have very useful properties.
  • The definition of a hydrocarbon is a compound that contains only hydrogen and carbon atoms.
  • There are different ways to represent organic compounds which are shown below.

Naming Organic Compounds

Homologous Series

  • This is a series or family of organic compounds that have similar features and chemical properties due to them having the same functional group.
  • All members of a homologous series have:
    • The same general formula.
    • Same functional group.
    • Similar chemical properties.
    • Gradation in their physical properties.
    • The difference in the molecular formula between one member and the next is CH2.
  • The names of organic compounds have two parts: the prefix or stem and the end part (or suffix).
  • The prefix tells you how many carbon atoms are present in the longest continuous chain in the compound.
  • The suffix tells you what functional group is on the compound.

Homologous_Series_Table, IGCSE & GCSE Chemistry revision notes

  • Some common structures in organic chemistry are shown below.

Structures, IGCSE & GCSE Chemistry revision notes

  • When there is more than one carbon atom where a functional group can be located, it is important to distinguish exactly which carbon the functional group is on.
  • Each carbon is numbered and these numbers are used to describe where the functional group is.
  • When 2 functional groups are present di- is used as a prefix to the second part of the name.
  • Branching also needs to be considered, the carbon atoms with the branches are described by their number.
  • When the location of functional groups and branches needs to be specified, the functional group takes precedence so it has the lowest number.
  • The table below illustrates the structures and names of some branched organic compounds.

Examples branched molecules, IGCSE & GCSE Chemistry revision notes

Composition of Crude Oil

  • Crude oil is also called petroleum and is a complex mixture of hydrocarbons which also contains natural gas.
  • Hydrocarbons are compounds that contain large molecules made of carbon and hydrogen only.
  • The hydrocarbon molecules in crude oil consist of a carbon backbone which can be in a ring or chain, with hydrogen atoms attached to the carbon atoms.
  • The mixture contains molecules with many different ring sizes and chain lengths.
  • It is a thick, sticky, black liquid that is found under porous rock (under the ground and under the sea).
  • Crude oil formed over millions of years from the effects of high pressures and temperatures on the remains of plants and animals.
  • Since it is being used up much faster than it is being formed crude oil is a finite resource.

Crude-oil-under-the-sea, IGCSE & GCSE Chemistry revision notes

Diagram Showing Crude Oil Under the Sea

Alkanes

Homologous Series

  • This is a series or family of organic compounds that have similar features and chemical properties due to them having the same functional group.
  • All members of a homologous series have:
  • The same general formula.
  • Same functional group.
  • Similar chemical properties.
  • Gradation in their physical properties.
  • The difference in the molecular formula between one member and the next is CH2.

The First Four Alkanes

  • The alkanes are a homologous series of hydrocarbon compounds with only single carbon bonds, there are no C=C bonds present.
  • The general formula of alkanes is:
    CnH2n+2
  • Alkanes are classified as saturated hydrocarbons as all the bonds in alkanes are single bonds.
  • They are colourless compounds which have a gradual change in their physical properties as the number of carbon atoms in the chain increases.
  • Alkanes are generally unreactive compounds but they do undergo combustion reactions, can be cracked into smaller molecules and react with halogens in the presence of light.
  • Methane is an alkane and is the major component of natural gas.
  • Methane undergoes complete combustion forming carbon dioxide and water:

CH4 + 2O2 → CO2 + 2H2O

  • The names and structure of the first four alkanes are shown below.

Alkane structures table, IGCSE & GCSE Chemistry revision notes

Table showing the formulae and structures of the first four alkanes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.