structure of 22BP4 is totally different with that of 44BP3 and 44BP4. As shown in
Fig. 3, the two opposite methylene bridges are oriented outwardly, and the other
two are oriented inwardly. The distances between the methylene bridges orientating outwardly and inwardly are 14.81 Å and 3.48 Å (Fig. 3b), respectively. In
addition, the 22BP4 molecules are racemic mixtures in the solid state (Fig. 3b).
Variable-temperature
1 H NMR spectra of 22BP4 in toluene-d 8 indicates that the
rotation is fast because no signal splitting or broadening is observed, even at
À60
C.
Fig. 2 Crystal structures of 4,4
0 -biphen[4]arene [25]
Fig. 1 Crystal structures of 4,4
0 -biphen[3]arene [25]
12 Biphen[n]arenes: Synthesis and Host–Guest Properties
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