Automerization is the name given to a process where carbon-ring chemicals tend to spontaneously transform into 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.