A<unk>  is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons. A<unk>  occupies a higher energy state than the corresponding non-excited nucleus, called the ground state. The<unk>  will eventually release the extra energy and decay into the ground state.
Nuclear isomer
Complex 
Heterocyclic compound
Mosaic 
Isomer
Cyclic compound
Diradical
Isotopomers