88812-39-9Relevant academic research and scientific papers
Spatial Structure of 4n? Helicene Dianions
Frim, R.,Goldblum, A.,Rabinovitz, M.
, p. 267 - 274 (2007/10/02)
Helicene dianions, e.g. phenanthrene derivatives, once believed to be non-helical, maintain their chirality as 4n? dianions.Phenanthrene 5, as well as substituted phenanthrene derivatives, undergo a two-electron reduction to form the respective 4n? dianion e.g. 52-/2Li+.Phenanthrene derivatives substituted at the 4- and 5-positions (bay substituents) e.g. 6-11, which are helical, afford stable dianions.These dianions are also prepared by a two-electron reduction of the (4n+2)? electron hydrocarbons and show, in their 1H NMR spectra, a quench of the paratropicity compared to 52- as well as a line shape dependence on their twist angle.The quench of paratropicity was also observed in the closely related charged helicenes derived from the benzochrysene system, i.e. anions 122- and 132-.The twist angles were calculated by MMX and MNDO calculations for the neutral systems, i.e., 5-11, and by MNDO for the dianions.MNDO calculations also included the preferred location of the counter cation.A dynamic NMR spectroscopic study proves experimentally the helicity of anion 112- thus shedding light on the behaviour of this novel class of dianions.
Liquid Chromatography on Triacetylcellulose, 6. Synthesis, Chromatographic Enrichment of Enantiomers, and Barriers to Enantiomerization of Helical Phenanthrenes
Scheruebl, Herbert,Fritzsche, Ursula,Mannschreck, Albrecht
, p. 336 - 343 (2007/10/02)
Enantiomerization barriers (Table 1) for novel 4,5-disubstituted phenanthrenes of types A and B have been determined by coalescence of 1H NMR signals or by thermal racemization of chromatographically enriched enantiomers.The barriers depend upon the size of the groups R = CMe3, Br, Me, Cl, OBz, in A and B, the behaviour of annelated benzo rings instead of R being particularly considered.
