The fullerenes react readily with a variety of reagents.' Following their reactions with NMR spectroscopy has not been easy. While the 13C NMR spectra of Cm and C70 are simple, spectra of reaction products are not, since the attachment of groups to the fullerene skeleton reduces the high symmetry. After chemical modification, the single resonance of Cm and the five peaks of C70 are replaced by many small peaks. It requires very long data acquisition times to obtain spectra of such products. The time can be decreased through the use of 13C-enriched fullerenes. However, if several products are formed or, as is common, bis-adducts are produced, assigning the carbon peaks is difficult or impossible. It is necessary to carefully separate the reaction mixtures and examine each pure product. NMR of other nuclei on substituents of the fullerenes in reaction products can be useful. However, even with 1H NMR there can be complications. Fullerenes tend to trap solvent in the lattice, and solvent protons can appear in the 1H spectrum. Reagents and byproducts generally give proton signals as well. In order to obtain good 'H NMR spectra of fullerene products, it is necessary to use thorough purification and drying procedures.Continuing our studies of endohedral fullerene compounds of noble gases? we have recently used high pressure and heating to introduce 3He into C a and C70, increasing incorporation levels to around 0.1 5%. 3 We have used this material to obtain the first 'He NMR spectra of helium compound^.^ Each helium-labeled fullerene gives a single sharp peak. Line widths can be under 1Hz. The large chemical shifts (Ca, -6.3 ppm; C70, -28.8 ppm from dissolved 3He as reference) show that there are substantial aromatic ring currents modifying the magnetic field experienced by the helium nucleus in the center of the fullerenes. We expected that altering the s-bonding structure of the fullerene through reaction would produce substantial shifts in the 3He peak.We have now verified this expectation. We have subjected a 3He-labeled fullerene mixture (about 70% C a r 30% c70) to the reaction conditions recently reported by Maggini, Scorrano, and (1) Euckminrterfulleren; Billup, W. E., Ciufolini, M. A., Eds.; VCH: New York, 1993. (2) Saunders, M.; Jim6nez-Vdzquez, H. A,; Cross, R. J.; Poreda, R. J. Science 1993, 259, 1428. (3) Saunders, M.; JimCnez-V6zquez, H. A,; Cross, R. J.; Mroczkowski, S.; Gross, M. L.; Giblin, D. E.; Poreda, R. J. J. Am. Chem. Soc. 1994, 116, (4) Saunden, M.; JimCnez-Vgzquez, H. A,; Cross, R. J.; Mroczkowski, S.; Freedberg, D. I.; Anet, F. A. L. Nature 1994, 367, 256. 2193-2194. Scheme 1 7" I /N\Pratos for the azomethine ylide addition to fullerenes to form N-methylpyrrolidines (Scheme 1). We heated 25 mg of the3He-labeled fullerene mixture with 2 equiv of N-methylglycine and 5 equiv of paraformaldehyde at reflux in benzene for 2 h. After removal of benzene, the reaction mixture was dissolved in CS2 and filtered through a small plug of activated charcoal/silica gel. No other separation or purification of...

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synopsisThe interaction of unsubstituted purine with polyuridylic acid in DzO solution a t neutral pD has been studied by high resolution proton magnetic resonance spectroscopy. The poly U proton resonances were shifted to higher fields by the added purine, indicating that purine binds to the uracil bases of the polymer by base stacking. Severe broadening of the purine proton resonances was also observed, providing strong evidence for the intercalation of purine between adjacent uracil bases of the polymer. The line widths of the poly U proton resonances were not noticeably broadened in the presence of purine; thus, the binding of purine to poly U does not result in a more rigid or ordered structure for the polymer.