C-60(NO2)(2): Quantum-chemical evaluations of structure, energetics, and vibrational spectra

The complete PM3 structural optimizations are reported for all 23 positiona l isomers of C-60(NO2)(2) and interesting symmetry reductions are found. Th ere are two low energy structures while all the remaining species are separ ated by more than 10 kcal/mol from the computed ground state. In the ground state the two nitro groups are placed in para position on one hexagon. The next lowest structure is produced by addition to one 6/6 (double) bond of the cage. The species highest in energy are separated by more than 50 kcal/ mol from the ground state. IR vibrational spectra are also predicted for th e low-energy structures.