Fullerene Isomerism: Isolation of C2v-C78 and D3-C78

摘要

Early reports on the formation of the higher fullerences C76, C78, C84, C90, andC94 by resistive heating of graphite stimulated theoretical calculations of possible cage structures for these all-carbon molecules. Among the five fullerene structures with isolated pentagons found for C78, a closed-shell D3h-isomer was predicted to form preferentially. Two distinct C78-isomers were formed in a ratio of -5:1 and could be separated by high performance liquid chromatography. The carbon-13 nuclear magnetic resonance (NMR) spectrum of the major isomer is uniquely consistent with a C2 upsilon-structure. The NMR data also support a chiral D,-structure for the minor isomer. The isolation of specifically these two isomers of C78 provides insight into the stability of higher fullerence structures and into the mechanism for fullerene formation in general.