1973 Volume 46 Issue 12 Pages 3831-3835
The NMR spectra of multilayered [2.2]paracyclophanes (I–XVI), in which benzene rings are closely stacked, have been examined. The assignment of the signals was made not only by integral strength, but also by solvent effect and the Nuclear Overhauser effect. The steric compression effect of transannular methyl groups on aromatic protons was observed in methylated cyclophanes. Enhanced ortho substitution shift was also observed. All the aromatic protons shift to remarkably higher field due to the anisotropy of stacked benzene rings as the number of layers increases. The shielding effect caused by these rings was empirically estimated.
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