Isomerisierung des cis , cis , cis , trans ‐[9]Annulen‐Anions

Abstract

lsomerization of the cis~isF,cis,trans-[9~Annulene AnionThe isomerization of the cis,cis,cis,trans-[9]annulene anion (2) into the thermodynamically more stable all-cis-[9]annulene anion (3) has been investigated kinetically under different conditions. The activation enthalpies vary between AG* = 29.6 and 34.8 kcal mol-'. It is shown that this reaction is catalyzed by acids and also by alkali metals. Since we cannot exclude catalysis in the case of 34.8 kcal mol-', this value represents a lower limit for the thermal isomerization. The photochemical isomerization is much faster than the thermal isomerization. The difference between topomerization and isomerization of 2 is mainly caused by a different degree of localization of charge in the transition states of both reactions: in contrast to the topomerization the isomerization requires complete localization of charge. The higher conformational and configurational mobility of uncharged annulenes compared to annulene ions is due to the high energy which is required even for partial localization of charge.Die quantitative Ermittlung der reversiblen konformativen und/oder reversiblen konfigurativen Beweglichkeit mit Hilfe der 'H-Kernresonanz-Spektroskopie lieferte zahlenmal3ige Abschatzungen der energetischen Verhaltnisse hei Annulenen. So konnten 0th und Sondheimer zwei Konfigurationsisomere des [14]Annulens (1-[14]-43 bzw. 1-[14]-21) ausmachen und die Freie Aktivierungsenergie AG* der konformativen wie auch der konfigurativen Mobilitat bestimmen z), ') G. Boche, H. Weber und A .

Reduction and oxidation of annulenes

“…19 An additional consideration when extending this reasoning to ionic annulenes, is the finding from an early application of NMR spectroscopy that the chemical shifts of protons in unsaturated molecules are also affected by the x-charge density at the carbon centers to which they are connected.14-16,20 The series of annulene compounds covered here ranges from such classical examples as [4]annulene (1, cyclobutadiene),21 [6]annulene (2, benzene), and [8]annulene (3, cyclooctatetraene),22-24 up to the l,3,7,9,13,15,19,21-octadehydro [24]annulene (41) 25 and the tetra-tert-butyl-1,16-bisdehydro [26]annulene (25). 26 In addition to the above mentioned annulene ions there is the well known series of odd-membered monocations and monoanions which comprises the cyclopropenium cation (9),27 cyclopentadienyl anion (10),28 tropylium cation (11),29 cyclononatetraenyl anion (12) [30][31][32][33] and their higher homologues. Those species which do not possess a neutral diamagnetic counterpart have been extensively reviewed together with the neutral annul-enes11,34-38 and will be omitted here.…”

To What Extent Can Nine‐Membered Monocycles Be Aromatic?

“…[9] For 1C(SnH 3 ) 2 , 1O, 1S and 1C(SiH 3 ) 2 , the C 2v ''out'' structures are 3.5, 4.2, 4.2 and 8.6 kcal/mol higher in energy, respectively, than the most stable geometries. [36] [Note that we find 1S to be nonplanar, contradicting the recent statement of Salcedo et al…”

“…Heteronins (1) are nine-membered heterocycles, π-isoelectronic with (CH) 9 Ϫ (1CH ؊ ). [1] These potentially aromatic 10π-electron monocyclic systems suffer from less strain than the ten-membered annulenes, e.g.…”

Nonafulvalen: Synthese durch oxidative Kupplung von Cyclononatetraenid und Valenzisomerisierung

“…Die spektroskopischen Vergleiche weisen somit das im K-Kontakt aus 3 gebildete Reaktionsprodukt klar als K-ccct-CNT (11, M = K) [ 191 aus und widerlegen die fruher in [8] postulierte Struktur des Bi(cyc1ononatetraenyI)diids 4. Damit lassen sich sowohl auffallige NMR-spektroskopische Befunde wie auch fruhere praparative Diskrepanzen zwanglos erklaren: Einmal ist einleuchtend, dass die oxidative Kupplung von 11 nichtwie ausgehend von 4 erwartet -Nonafulvalen, sondern Bi(cyclononatetraeny1) 3 ergibt; sodann erweist sich der 'uberraschende Zerfall von 4 in Gegenwart von Kaliummetall' [8] als die bekannte und von Boche et al [20] eingehend untersuchte Isomerisierung 11-+2, die durch Alkali-Metalle katalysiert wird.…”