Endohedral Helium in Fullerenes - an Internal Probe

He C6o and He C7o The He NMR spectra of endohedral helium atoms were used to monitor the aromaticity of the fullerenes as a function of electron addition upon reduction. The reduction of He C6o and He C7o to their hexaan-ions was followed by a study of their He shifts [17]. The reduction was carried out with Li metal (in the presence of 2), and the NMR spectra of the anions were 

These NMR experiments confirmed the conclusions of several calculations regarding fullerene anions. Intensive computational research was done into the spherical aromaticity of fullerene and fiiUerene anions and is summarized in the 2001 review by Bilhl and Hirsch [154]. The London calculations on Qo predicted only diatropic ring currents, a large diamagnetic susceptibility and a huge endohe- 

Comparison of the He NMR chemical shifts of the neutral fullerenes and their anions shows that the changes in the chemical shifts are different from one fullerene to another. While the He bands of C78-D3, Cg4 and C76 are shifted to a higher field as a result of their reduction (similar to Ceo), those of the two isomers of 7  

Two helium atoms inside fullerenes Another signal that was measured in the He NMR spectra is that of two helium atoms inside a fullerene, e.g. He2 C .  

The degree of deshielding is different from one fullerene to another, where the 

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