Nonapentafulvalene(1) has been prepared by oxidative coupling of sodium cyclopentadienide (6) and sodium cyclononatetraenide (7) with CuCl2in THF, two‐fold deprotonation of cyclopentadienyl‐cyclononatetraene8to give dianion16, and oxidative treatment of16with CuCl2(Schemes 2and3). Compound1is a highly reactive and thermally instable molecule, since valence isomerisation1→17proceeds easily even at low temperature (the half‐life of1isca.30 min at −15° in CDCl3). NMR investigations show that nonapentafulvalene is an olefinic molecule with strongly alternating bond lengths, its nine‐membered ring deviating strongly from planarity. Comparison of the NMR data of1with those of a series of sterically similar pentafulvenes18and nonafulvenes19(Tables 1and2) demonstrates that (a) with regard to the pentafulvene unit of1, the cyclononatetraene ring acts as very weak electron‐donating group, while (b) with regard to the nonafulvene unit of1, the cyclopentadiene ring acts as weak electron‐accepting group. So nonapentafulvalene may be regarded as a ‘nonafulvene of inver