C54N6 A POTENTIALLY AROMATIC MOLECULE

Relative energies for the D-3d and D-3 symmetric isomers of C54N6 are approximate to 76 (1), 100 (2), 44 (3), 0 (4), 43 (5), and 30 kcal/mol (6) at the SCF/3-21G//SCF/3-21G level. D-3d symmetric isomers 1 and 2 exhibit endohedral He NMR chemical shifts of approximate to -63 ppm (GIAO-SCF/tzp(He)dzp(C, N)//SCF/3-21G level), reminiscent of the highly aromatic, isoelectronic C-60(6-) (-67 ppm). Although more stable than 1 and 2, D-3 symmetric isomers 3-6 are indicated to be less aromatic, according to the computed endohedral chemical shifts, delta(He) approximate to -12 to -28 ppm. Formation of 4 from trimerization of NC-(CC)(8)-CN is highly exothermic, but recent experiments suggest large barriers for such a process.