13C NMR chemical shift assignments for 1,2-C60H2 (1) and a series of 13C-labeled fullerene derivatives with three-, four-, and five-membered annulated rings (2-4) were assigned using 2D INADEQUATE spectroscopy and examined for trends that correspond to the changes in strain in the fullerene cage. Chemical shifts of equivalent carbons from 1-4 show that eight carbons trend downfield (carbons 5, 7, 8, 9, 11, 15, 16, 17) and the remaining six carbons (4, 6, 10, 12, 13, 14) trend upfield with increasing ring size. While the average chemical shift is nearly constant, the dispersion is greatest when the local strain is the least, in 1,2-C60H2 (1). 13C chemical shifts are not well correlated with trends in ring size, with strain as measured by the pyramidalization angle of nearby carbons, or with the geometry of the fullerene cage. We interpret the results as evidence that subtle geometrical changes lead to modulation of the strength of ring currents near the site of addition and, in turn, the magnetic field generated by these ring currents affects the chemical shift of carbons on the far side of the fullerene core. These results highlight ring currents as being critically important to the determination of 13C chemical shifts in fullerene derivatives.
Thermal Diels-Alder reactions between C(60) and electron-deficient 3, 6-diaryl-1,2,4,5-tetrazines yield monoadducts possessing a diaryldihydropyridazine function nested atop the fullerene. The diaryldihydropyridazine functions direct a completely regioselective 1,4-hydrogenation, resulting in a racemic mixture of bifunctional bisadduct (+/-)-3.
C60-tetrazine Diels-Alder adducts bearing electron deficient dihydropyridazine groups undergo chemoselective amination and hydration reactions upon addition of primary aliphatic amines and water, respectively, to form new adducts with 4,5-dihydropyrazole groups nested atop the [60]fullerene skeleton.
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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
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