Why can't antiaromatic compounds just escape planarity and become non-aromatic to avoid destabilization?

Question

Why can't just all anti-aromatic systems lose planarity (and hence conjugation) and be non-aromatic like cyclooctatetraene ? Would they not be more stable that way? Because anti-aromatic systems tend to be highly destabilized. What can be a good working rule to predict whether an anti-aromatic system will remain anti-aromatic or whether it will somehow manage to lose planarity and become non-aromatic?

Answer 1

These types of rings do tend to pucker out of planarity, as you have described. You're exactly right that by breaking perfect planarity, the conjugation is decreased, thereby decreasing the anti-aromaticity of the system, and helping it to be less unstable.

However, due to the constraints on bond angles imposed by the orientation of sp2 orbitals that overlap to form sigma bonds, the ring can't just take on any shape it chooses to fully get out of anti-aromaticity. It will strike a balance between the energetic penalty of straining its bond angles and that of being anti-aromatic.