Lithium reduction of the bowl-shaped C-60 fragment diindeno[1,2,3,4-defg; 1 ',2 ',3 ',4 '-mnop]chrysene: An interplay between experiment and calculation

Diindeno[1,2,3,4-defg;1 ' ,2 ' ,3 ' ,4 ' -mnop]chrysene (DIC) (one of the s mallest symmetrical bowl-shaped fragments of C-60) and its tetra-tert-butyl derivative are reduced with lithium metal to yield dianions and tetraanion s. Due to the high degree of symmetry (C-2v) of DIC and its derivative, the ir NMR spectra cannot be assigned using the standard two-dimensional NMR te chniques. A novel carbon-edited NOESY method was used to complete the assig nments of the neutral and dianion species, whereas the tetraanions are aide d by DFT calculations for their assignment. Experimental charge-distributio n patterns were obtained and match those of the calculations. An extension of the empirical approach for estimating the charge distribution from the C -13 NMR spectra enables a direct comparison between experimentally derived charge-distribution data and the computed electron density in each of the l owest unoccupied molecular orbitals. The overall picture evolving from the orbital structure of DIC is presented and reflects the surface reactivity o f C-60.