Necessary conditions for the pi-electron delocalization in enamino-type muscle relaxants

Two necessary conditions have been proposed for the pi-electron delocalization across four bonds in bis-quaternary bromides of enamino spiro-ketal-type compounds. Dynamic NMR data analysis of these compounds suggests that pi-electron delocalization takes place if the first atom is nitrogen and the fourth atom is either nitrogen or oxygen [i.e., N+ = C-C = N (or O)]. The second condition is that the end atoms of the four-bond system should not be the terminal group.