3576
J. Phys. Chem. 1992, 96, 3576-3578
could be due either to decreased isotope scrambling in the adduct, increased contribution from CT, or perhaps to an additional high-energy scattering process. The isotope distribution for C5*+provides further insight into the scattering mechanism. This endoergic fragmentation channel is expected to require an intimate collision, which may or may not involve formation of a [c6]+]*intermediate complex. Figure 2f shows that for a collision energy of 33.5 eV, C5*+usually retains the 13C,demonstrating that the fragmentation mechanism includes formation of an intermediate complex where isotope scrambling can occur.
Conclusions We have demonstrated that C+ and C, react with no activation
energy, to produce a C6,+species which is bound strongly enough to survive for milliseconds with up to 10 eV excess energy. The nature of this Cbl+adduct is such that I3Cisotope scrambling can occur, suggesting that the added atom is intimately bonded with or "incorporated" into the fullerene network. Further work is underway to extract the Cm+< binding energy, and to study C2+ addition fullerenes. Acknowledgment. We thank the Stony Brook machine shop for their efforts in producing the instrument, and Mark Ross and Harry Kroto for helpful discussions. This work is sponsored by the Office of Naval Research (N00014-85-K-0678 and URIP NOOO- 14-86-G-0208).
ESR Studies of the Reaction of Alkyl Radicals with Csot J. R. Morton,* K. F. Preston,* Steacie Institute for Molecular Sciences, National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario, Canada K l A OR9
P. J. Krusic,* S. A. Hill, and E.Wasserman Central Research and Development, E . I. du Pont de Nemours & Company, Wilmington, Delaware 19880-0328 (Received: February 20, 1992)
Photolytically and thermally generated alkyl radicals (R' = tert-butyl, 1-adamantyl, isopropyl, ethyl, and benzyl) react with C60to form R-Cm* radical adducts which have been identified by the proton and I3C hyperfine interactions obtained from their electron spin resonance spectra. Consideration of the I3C spectra shows that the unpaired electron in R-Cm* is mostly confined to two fused, six-membered rings on the Cm surface, having the substituent R at one of the points of fusion. Each half of the resulting radical structure of C, symmetry can be compared with a cyclohexadienyl radical. Extensive delocalization of the unpaired electron over the Cm sphere is ruled out.
The chemistry of Cm is still in its infancy. So far, there have been relatively few reports of chemical modifications of C,. These include the Birch reduction to C60H36,1the formation of organometallic derivatives? alkylation? halogenation? epoxidati~n,~ and the addition of C(C6H5)2groups across double bonds of the c 6 0 frameworkn6 We have detected by ESR and mass spectrometry radical derivatives of Cm such as (C6H5CH2),Cm'and (C6H5CH2)5C60'.7It seems inevitable, however, that the chemistry of Cb0and other fullerenes will develop rapidly. Further developments in the chemical manipulation of C, will undoubtedly be aided by an improved understanding of the factors governing the initial attachment of a chemical reactant to a single carbon of this spherical molecule. We now report the observation by ESR of such a basic step: the addition of a single alkyl radical (R') to the CM molecule. The ESR spectrum of the tert-butyl radical adduct (CH3)$C60* can be obtained by several photochemical and thermal methods including the UV irradiation a t 323 K of a saturated solution of Csoin benzene containing tert-butyl bromide.*-I0 The spectrum is remarkably persistent after irradiation and shows a 10-line hyperfine manifold (Figure 1A and insert) having the binomial intensity distribution appropriate for nine equivalent protons interacting with a single unpaired electron (a(9H) = 0.17 f 0.01 G)." At high gain, several pairs of satellite transitions due to I3C ( I = in natural abundance can be seen in the wings of the spectrum. To aid the 13Chyperfine analysis, the perdeutero analogue was generated by photolysis of di-tert-butyl peroxide in benzene containing Cm and perdeuterioisobutane (eqs 1-3).'2 'NRCC Contribution No. 6184, Du Pont no. 32964.
(CH3)3CO-OC(CH3)3 (CH,),CO'
+ (CD3)3CD c60
-.c
2(CH3),CO'
(CH3)3COD
+ (CD.3)jC'
+
(1)
+ (CD3)3C'
(CD3)3C
