On aromatic stability of oxygen- imino-, and sulfur-bridged [18]annulenes

Oxygen-, imino-. and/or sulfur-bridged 18]annulenes are studied using the A_s-index of aromatic stabilization. Theoretical predictions, which indicate that these compounds should differ among themselves in their aromatic properties, correlate nicely with the available experimental findings. Unknown compounds of this class: 18]annulene imino-dioxide and 18]annulene oxide-imino-sulfide are predicted to be aromatic and good candidates for preparation. The same prediction is also reached for 1,10-diaza18]annulene.