Basic Organic Nomenclature

An Introduction

Dave Woodcock,
Associate Professor Emeritus UBC (Okanagan)
©1996,2000, 2008

1. The IUPAC Sysematic Approach
I. The How and the Why


'The Why' :
Naming untold numbers of compounds!

    The carbon atom is unique in its bonding in that it can form stable molecules consisting of chains of carbon atoms of any length. Coupled with the observation that each carbon atom forms four bonds to other atoms this leads to incomprehensibly large numbers of possible molecules.

    To be able to name such vast numbers of possible molecules requires a systematic approach consisting of a set of arbitrary rules which are readily learned and applied to each molecule individually to generate the name.

    The IUPAC nomenclature system is such a set of rules used widely by organic chemists and this introduction to nomenclature will outline the rules in this sytem for the simpler organic compounds.

    Note that in addition to names invented for compounds because of their origin, there were other attempts to produce a systematic nomenclature system before the IUPAC system and sometimes compounds have several different names, of which the IUPAC name may not be the one most commonly used.

'The How' :
The two basic features of the IUPAC name.

    Because every organic compound contains carbon, and almost every one contains hydrogen, the names of these two elements do not appear directly in the compound names. Instead the IUPAC system names a compound based on the number of carbon atoms linked together in the longest continuous chain of carbon atoms.
    This is the first feature used in forming the IUPAC name.

    The second feature arises from the observation that different organic compounds containing similar carbon or non-carbon groups (so-called functional groups) within the the molecules react similarly. This leads to the compounds being grouped in families according to the functional groups that they contain, and gives a second characteristic to be used in the IUPAC name.

At its simplest, the IUPAC name for an organic compound contains these two parts:
    a root indicating how many carbon atoms are in the longest continuous chain of carbon atoms

    a prefix and/or suffix to indicate the family to which the compound belongs.

For example, the name ethanol (image below)indicates a carbon chain of length two (root: eth-) and an OH functional group (suffix: -anol).

Self Test Questions:
Next Page: Root Names.


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