Aromatic compounds are cyclic, conjugated polyenes with planar configuration. They follow Huckel's rule (meaning that they must have 4n + 2 pi electrons (n = any nonnegative integer)). So for example benzene is aromatic because it has 6 pi electrons (n = 1). Antiaromatic compounds are cyclic, conjugated polyenes with planar configuration, that have 4n pi electrons..
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Aromatic compounds are cyclic, conjugated polyenes with planar configuration. They follow Huckel's rule (meaning that they must have 4n + 2 pi electrons (n = any nonnegative integer)). So for example benzene is aromatic because it has 6 pi electrons (n = 1). Antiaromatic compounds are cyclic, conjugated polyenes with planar configuration, that have 4n pi electrons..
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Oh sorry, I forgot to explain non-aromatic compounds. They are conjugated polyenes that do not fall into the category of aromatic or antiaromatic. Either because they do not possess either 4n + 2 or 4n pi electrons, or because they are not planar or completely conjugated. So for example cyclooctatetrane (conjugated 8 member ring) is non-aromatic because even though it has 4n electrons, it is not planar.
The best way to get n is to start by counting how many pi electrons there are in the compound. (Double bonds and electron pairs count for 2, heterocyclic atoms are a bit trickier). Then take the number of pi electrons in the compound subtract 2 and then divide by 4. That will give you n, if it is a positive integer or zero, then the compound is aromatic.
