In chemistry, 'organic' was a term first applied by Jöns Berzelius to compounds, such as sugars and alcohols, which occur naturally in plant and animal 'organisms.' At the time, there was considered to be a fundamental difference between organic and inorganic materials. In modern parlance, organic refers to the chemistry of carbon, with the exception of a few simple carbon compounds.


Medically, 'organic' means to do with any or all of the organs of the body.


Chemistry of organic compounds

The majority of organic compounds are made up from two different sorts of unit – a hydrocarbon chain or ring together with one or more active groups. The chemical behavior of a substance depends mainly upon the active group, and whether the group is attached to a chain or ring of carbon atoms.


However, the behavior of the group is modified by the length of the hydrocarbon chain. If there are two or more active groups in the molecule, the properties of the substance also depend upon the relative positions of these groups. In particular, the hydrocarbon part of the molecule determines the physical properties (melting point, solubility, etc) of the compound.


For instance, ethanoic acid (also called acetic acid) and butanoic acid (butyric acid) are both carboxylic acids (they contain the –COOH group) and react with ethanol (ethyl alcohol) to form esters However, butanoic acid contains a longer hydrocarbon chain than does ethanoic acid – the boiling point of butanoic acid (with its three unit chain) is 16°C, while ethanoic acid (with its single unit) boils at 118°C. In general, the boiling point rises as the length of chain increases.


The hydrocarbon part of the molecule may have its skeleton a chain or a ring of carbon atoms – the chemical reactions which the substance will undergo are also influenced by the type of hydrocarbon units. For instance, ethanol is a chain (or aliphatic) compound contain an hydroxyl (-OH) group. The corresponding ring (or aromatic) compound containing one hydroxyl group is phenol. Ethanol is neutral but phenol is weakly acidic.


Important organic groups include:


amino group
carbonyl group
carboxyl group
hydroxyl group
nitrile group
organic halides