1H and 13C nuclear magnetic resonance reinvestigation of the dibenzo[a,c]cyclononatetraenyl anion and its 5,9-diphenyl derivative. Planarity vs nonplanarity

It is found that the dibenzo[a,c]cyclononatetraenyl anion is readily transformed into the stable 1H-cyclopenta[l]phenanthren-1-yl anion. Earlier reported NMR data of this compound were incorrectly assigned to a planar structure of the dibenzocyclononatetraenyl anion. The nonplanarity of the initially formed nine-membered ring anion was confirmed both experimentally and theoretically. The ring-closure process does not take place in the anion of the 5,9-diphenyl derivative, which retains a nonplanar conformation of the nine-membered ring. 17 references, 2 figures, 1 table