To determine if a compound is aromatic, one must check for: 1. Cyclic Structure The molecule must be cyclic. 2. Planarity The ring system must be planar to allow for effective pi electron overlap. 3. Delocalized Pi Electron System There must be a continuous ring of p orbitals that allows for delocalization of pi electrons. 4. Hückel's Rule The number of pi electrons in the delocalized system must follow the (4n+2) rule, where n is a non-negative integer (0, 1, 2, ...). This means 2, 6, 10, 14, etc., pi electrons. If any of these criteria are not met, the compound is not aromatic. It could be anti-aromatic (if it has 4n pi electrons) or non-aromatic.