Automerization is the name given to a process in which carbon-ring chemicals tend to spontaneously transform into closely-related chemicals when heated.

The first example found was the transformation of azulene to naphthalene.

The 'reactions' involve a re-arrangement (so called 'scrambling') of the atoms in the chemicals' carbon ring.

[…] since the characterization of the automerization of naphthalene by Scott in 1977, similar atom scramblings of other aromatic hydrocarbons such as pyrene, azulene, benz[a]anthracene and even benzene have been described. While the existence of these reactions has been confirmed, the isomerization and automerization mechanisms remain unknown.
See: Wikipedia

Note: Various mechanisms have been proposed to explain the changes - some at quantum level, e.g. 'carbon tunnelling' - but none has been formally adopted.

Also see: Benzene structureplugin-autotooltip__plain plugin-autotooltip_bigBenzene structure

The benzene molecule is composed of 6 carbon atoms joined in a ring with 1 hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon.

Although the compound has been very extensively studied since its first isolation in 1825, its molecular dynamics - especially at temperatures below 77K when it becomes a solid - are extremely complex and the underlying atomic mechanics are for the most part still obscure.