Classifying And Naming Organic Compounds

Organic chemistry is the chemistry of carbon compounds, except for the very simplest such as oxides and carbonates.  There are more carbon compounds than the compounds of any other element because carbon atoms have a remarkable ability to join up in stable chains and rings.

There are literally millions of organic compounds and to avoid any confusion or difficulty in naming them as they are discovered an international body of chemists drew up an internationally accepted set of rules for naming these compounds.  This body became known as IUPAC, which stands for International Union of Pure and Applied Chemistry.

 In order to learn the names of organic compounds in GCSE chemistry it is best to learn some of their rules, just to make it easier.  Most of these names can be broken into two parts, the second part can, in turn, be separated into two further parts.

Assigning the prefix.

This is simply based on the number of carbon atoms in the longest chain of the molecule.

Assigning the suffix.

The many millions of organic compounds can be divided up into a number of different families of compounds, which are actually called homologous series.  Their names come from splitting the suffix into two parts:

First part:

Indicates if there are any double, or triple bonds in the chain:

All single bonds then the suffix begins with; -an-

A double bond is shown with the suffix beginning with; -en-

A triple bond is shown with the suffix beginning with; -yn-

N.B. The triple bond does not need to be known at GCSE level.

Second part, is the ending which shows what is joined to the carbon chain, i.e. if only hydrogen is added to the chain then the last part of the suffix is –e.  If a hydroxyl group is the last part of the chain then the suffix ends with –ol.  If the organic molecule is an acid then the last fragment of its suffix is –oic.

Example of organic nomenclature.

The number of carbon atoms in the molecule is 1, so its prefix is meth.  It contains only single civalent bonds, so the first part of its suffix is –an, and its suffix ends with –e because the molecule contains only hydrogen with carbon.  Therefore the molecule’s IUPAC name is methane.

 By Ciaran Flynn: Loreto College, Coleraine.