The proton NMR magnetic shieldings of the recently synthesized D_3d isomers of methylene-bridged [6]cycloparaphenylene (MB[6]CPP) and [12]cyclophenacene hide in themselves the effect of a global paratropic current around the nanobelts, which is induced by a magnetic field parallel to the main symmetry axis of the molecules. The effect is particularly pronounced for the methylene protons of MB[6]CPP, especially for those facing inside the nanobelt. The small experimental chemical shift difference of only 0.2 ppm is incompatible with the separation of the signals caused by the belt curvature, which, by itself, is calculated to be larger than 1 ppm, with both signals shifted upfield with respect to the position detected for the nanobelt. A careful dissection of the proton magnetic shielding in terms of molecular orbital contributions, has permitted a quantitative assessment of the genuine effect on each different proton caused by a substantial paratropic belt-current, which brings all the signals in nice agreement with the experimental spectra.

中文翻译：

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弄清楚碳纳米环和纳米带中质子磁屏蔽的贡献：抛物线带电流的证据。

最近合成的D _3d的质子NMR磁屏蔽亚甲基桥连的[6]环对亚苯基（MB [6] CPP）和[12]环并苯的异构体本身隐藏了围绕纳米带的整体抛物线电流的影响，该电流是由平行于纳米带主对称轴的磁场感应产生的分子。对于MB [6] CPP的亚甲基质子，尤其是面向纳米带内部的亚甲基质子，该效果尤为明显。仅0.2 ppm的小实验化学位移差异与皮带曲率引起的信号分离不兼容，皮带曲率本身被计算为大于1 ppm，两个信号都相对于检测到的位置向高场偏移纳米带。根据分子轨道的贡献仔细剖析质子磁屏蔽，