Those of you who posted after adrian don't seem to have understood xyr explanation. Aromatic systems always have 4n+2 pi electrons, or 2n+1 pi bonds, with n being zero or a positive integer. Because C has 4 pi electrons (2 pi bonds) it is not aromatic;
4(0)+2 = 2
4(1)+2 = 6
There's no way to get 4 from 4n+2 if n's an integer. All the others have the proper number of pi electrons/bonds.
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