[10]annulenic perimeters Similar to the [14]annulenes, a number of [10]annulene perimeters have been reported based on naphtalene and azulene motifs. These have similar aromatic structures as their [10]annulene perimeters also contain 4n+2 πelectrons. We find several bridged naphthalene analogs where the first excited state is a Hund's rule violation (Figure ). However, all azulene analogs we have tested obey Hund's rule; for example, the azulene analog in which the bond shared by the 5-and 7membered rings is replaced by a methylene moiety is shown in Figure .