[constantly_planck]

Okay, so this is my first post so bear with me if I'm screwing anything up. So I'm in my second semester of organic chemistry and the topic is dienes, resonance, aromaticity, and the diels-alder reaction. Everything makes sense and is fairly simple but there's one thing bugging me: how can you tell if a molecule is planar when determining aromaticity? I'm especially having problems with ions and free radicals. I get that sp3 atoms aren't going to be planar but if I can create a resonance structure where I can turn the ion/radical into an sp2 atom does that automatically mean that it's planar? I'm really having trouble when an oxygen and a nitrogen are next to each other on a six membered ring, since an oxygen with two lone pairs would be sp3. Please use help me with your chemistry superpowers!

[AWK]

https://www.wikiwand.com/en/Antiaromaticity

[orgopete]

This is how I consider it. Aromatic is a low energy form and anti-aromatic is simply a higher energy form. If sufficient forces can be brought to bear, then it may be possible to find an example of an anti-aromatic compound, such as a cyclobutadiene. However, if a molecule can adopt a conformation or the stereoelectronics of a molecule are such that the electrons cannot be shared, then it can be aromatic, non-aromatic or anti-aromaticity may not be an issue.

For example, the non-bonded electrons of pyridine are orthogonal to the pi-electrons of the ring and it therefore is aromatic. The non-bonded electrons of furan can adopt a conformation that allows them to participate in a now lower energy aromatic form. Now, when you get to cyclooctatetraene, if planar, anti-aromatic, however, it can adopt a non-planar conformation and therefore is non-aromatic.