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7. The two principal conformations of overcrowded ethylenes: folded (a) and twisted (b), reproduced from reference 48d.
Source publication
![Table 1 : Calculated lengths and twist angles of the central bond. [a]](profile/David-Eisenberg/publication/230626684/figure/tbl1/AS:669485254078468@1536629131281/Calculated-lengths-and-twist-angles-of-the-central-bond-a_Q320.jpg)
Citations
... Reduction with lithium metal was performed in THF-d 8 , under vacuum, as described elsewhere. [33] [50] [52] NMR experiments were performed with a Bruker AVII 500 MHz spectrometer, with a z-gradient coil with maximum ...
... We suggest a general explanation for these observations along the following lines. First, bowl-to-bowl inversion in a singly substituted corannulenyl is weakly influenced by the nature of the substituent, as known from many literature examples [22] including our own studies of oligocorannulenyls 2 and 3. [50] [51] [52] [53] Thus, it can be assumed that the bowl-to-bowl inversion freezes near 240 K. Second, analysis of the optimized geometry of 4 reveals that the corannulenylphenyl unit is structurally similar to its analogue in 3. As a result, energy barriers for rotation, arising from collision between the corannulenyl and phenyl protons, are expected to be very similar. ...
... In previously studied oligocorannulenylic stacks, such as (2 8– ) n and (3 8– ) m , supramolecular oligomerization prevailed , with n = 2–7 and m = 2–11. [50] [52] [53] However, the 1 H-NMR spectra of (2 8– ) n and (3 8– ) m exhibited broad and irregular resonances at room temperature, whereas 4 12– exhibits uncommonly sharp peaks. Thus, it is possible that a narrow size distribution of (4 12– ) x stacks exists in solution, and complex stereochemistry accounts for the multitude of resonances. ...
Oligocorannulenes are polyarenes composed of several corannulene units that are covalently linked. Their behavior arises both from the diverse properties of each corannulenyl unit and from the interactions between them. In this paper, we present the synthesis, stereochemistry, reduction, and self‐assembly properties of a novel type of oligocorannulene: branched 1,3,5‐tricorannulenylbenzene. Several stereodynamical elements combine to give rich stereochemistry: bowl‐to‐bowl inversion, rotation about the aryl‐aryl single bonds, and residual stereoisomerism of molecular propellers. Reduction with lithium metal yields an intermediate hexaanion and ultimately produces a highly charged dodecaanion. Self‐diffusion NMR demonstrates that the dodecaanion undergoes supramolecular dimerization through charged polyarene stacking, wherein two molecules are linked at all three contact points. The preference for dimerization over dendrimerization is attributed to an entropic effect. The dimer is found to undergo complex structural dynamics, as well as ion‐pairing dynamics, as revealed by variable‐temperature 1H‐ and 7Li‐NMR. Copyright © 2012 John Wiley & Sons, Ltd.
