| Abstract
| - Isomers of C60H36 and He@C60H36 have been synthesized by the Birch or dihydroanthracene reductionof C60 and isolated by preparative high-pressure liquid chromatography. 3He, 13C, and 1H NMR spectroscopicproperties were then determined. A comparison of experimental chemical shifts against those computed usingdensity functional theory (B3LYP) with polarized triple- and double-ζ basis sets for He and C,H, respectively,allowed provisional assignment of structure for several isomers to be made. Theoretical calculations have alsobeen carried out to identify low-energy structures. The transfer hydrogenation method using dihydroanthracenegives a major C60H36 isomer and a minor C60H36 isomer with C3 symmetry as determined by the 13C NMRspectrum of C60H36 and the 3He NMR spectrum of the corresponding sample of 3He@C60H36. In view of theHPLC retention times and the 3He chemical shifts observed for the Birch and dihydroanthracene reductionproducts, the two isomers generated by the latter procedure can be only minor isomers of the Birch reduction.A significant energy barrier apparently exists in the dihydroanthracene reduction of C60 for the conversion ofthe C3 and C1 symmetry isomers of C60H36 to the T symmetry isomer previously predicted by many calculationsto be among the most stable C60H36 isomers. Many of the 1H NMR signals exhibited by C60H36 (and C60H18,previously reported) are unusually deshielded compared to “ordinary” organic compounds, presumably becausethe unusual structures of C60H36 and C60H18 result in chemical shift tensors with one or more unusual principalvalues. Calculations clearly show a relationship between exceptionally deshielded protons beta to a benzenering in C60H18 and C60H36 and relatively long CC bonds associated with these protons. The additionalinformation obtained from 1D and 2D 1H NMR spectra obtained at ultrahigh field strengths (up to 900 MHz)will serve as a critical test of chemical shifts to be obtained from future calculations on different C60H36isomers.
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