Why Antiaromatic Compounds Are Unstable?

Antiaromaticity is so destabilizing that it can cause compounds such as cyclobutadiene to elongate or manipulate their orbitals so that the pi system is no longer aromatic.

Why antiaromatic compounds are highly unstable?

Antiaromaticity is a characteristic of a cyclic molecule with a π electron system that has higher energy due to the presence of 4n delocalised (π or lone pair) electrons in it. ... To avoid the instability of antiaromaticity, molecules may change shape, becoming non-planar and therefore breaking some of the π interactions.

Why non aromatic compounds are more stable than antiaromatic?

It is shown that the antiaromatic compound is more stable than the non aromatic compounds 2 and 3 because of a more conjugated system. Here's the exact statement: In the first structure, delocalization of the positive charge and the π bonds occurs over the entire ring.