How to Identify Ortho, Meta, Para on a Benzene Ring

As an organic chemistry student you will be faced with the challenge of naming organic compounds using both IUPAC nomenclature and common names. Your professor will likely point out which option to use for each type of naming

Substituted aromatic compounds follow a unique naming method particularly when naming a molecule with 2 substituents

Ortho, Meta, Para

Sure you can follow the standard numbering and naming system, however the ortho, meta, and para system allows you to simplify the compound name by replacing the number of each substituent with a simple designation

The first step is to identify your parent chain, in this case the benzene ring, and locate your highest priority group to be your functional group. This will be the understood position number 1.

When counting your substituent in reference to your functional group it doesn’t matter if you have to count clockwise or counterclockwise. Remember that benzene is an aromatic compound which means that every atom is sp2 hybridized and trigonal planar (aka flat) If you have a substituent on the right of a flat molecule it winds up on the left for a non-flat molecule

From this point you simply apply the following designations:

Ortho: 1 carbon away from your primary carbon, or position #2

Meta: 2 carbons away from your primary carbon, or position #3

Para: 3 carbons away from your primary carbon, or position #4

Since benzene has a total of 6 carbons, when the first is assigned the primary carbon you will have the option for 2 ortho positions, 2 meta positions, but only 1 para position that is directly opposite from your molecule.

How to Identify Ortho, Meta, Para on a Benzene Ring