title: Reactions of C70(2-) with organic halides revisited: unusual magnetic equivalence for the diastereotopic methylene protons in 2,5-(PhCH2)2C70.
abstract: The reactions of C70(2-) with organic halides result in several isomeric products. However, the structures of the isomers have not been identified unambiguously and the reactions still remain elusive even though the first report of the reaction appeared more than ten years ago. Herein, the reactions of C70(2-) with ArCH2Br (Ar = Ph, o-, m-, and p-BrC6H4) are revisited. Two types of isomeric para-adducts of 2,5- and 7,23-(ArCH2)2C70 are obtained and characterized with the X-ray single-crystal diffractions, HRMS, (1)H and (13)C NMR, and UV-vis spectroscopies. An unusual singlet resonance instead of the typical AB quartet resonance is shown for the C2 diastereotopic methylene protons in (1)H NMR spectrum of 2,5-(PhCH2)2C70 recorded at ambient temperature. The unexpected magnetic equivalence is studied with the variable-temperature (VT) NMR and density functional theory (DFT) calculations. The results show that the greater local curvature in the C70 polar region is likely responsible for the unusual magnetic equivalence exhibited by the C2 diastereotopic methylene protons of 2,5-(PhCH2)2C70, indicating that under certain cases, it is improbable to elucidate the spectral data of fullerene derivatives with a less symmetrical carbon cage in analogy with those of the C60 derivatives.
authors.affiliation: State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, University of Chinese Academy of Sciences, 5625 Renmin Street, Changchun, Jilin 130022, China.
authors.forename: Shu-Hui
authors.initials: SH
authors.lastname: Li
authors.forename: Zong-Jun
authors.initials: ZJ
authors.lastname: Li
authors.forename: Wei-Wei
authors.initials: WW
authors.lastname: Yang
authors.forename: Xiang
authors.initials: X
authors.lastname: Gao