Is the C₈ring nonplanar?

Abstract

The second order Moller-Plesset (MP2) perturbation treatment with the 6-31 G* basis set was applied to the cyclic structure of Cs. It has been found that its minimum energy structure is nonplanar, possessing D2d point symmetry. The nonplanar species is located about 56 kJ mol-l below a planar cyclic stationary point. The latter structure has C4h symmetry and exhibits two imaginary vibrational frequencies. This finding reveals a distinct difference in the potential hypersurface topology resulting from the correlated MP2 and SCF approaches (as in the SCF/6-31G* treatment the C4h species is a local energy minimum). The MP2/6-31G* geometry, energy, and harmonic vibrational characteristics are reported.

A nonplanar cyclic minimum-energy structure of singlet C9

“…Nevertheless, one symmetry plane has emerged from the search (the symmetry plane superimposes four pairs of atoms (figure 1), so that we deal with a C s species. In contrast with the planar Cv minimum [20] and agreement with the nonplanar C8 minimum [21] found at the same level of theory, this C9 cycle is somewhat distorted from planarity (table 2). It is located some 26 kJ mol-1 above the linear species [12].…”

“…In view of the previous results on Cv [20] and Cs [21] the search for a nonlinear isomer of C 9 was concentrated on a cyclic species, although not necessarily planar (figure 1). Planar cyclic stationary points could be located, and even two different species (figure 2).…”

“…The computations were partly carried out with the Gaussian 90 [43] and partly with the Gaussian 92 [44] [12,20,21] the standard 6-31G* basis set was applied and the electron correlation was treated through all-electron second-order Moller Plesset (MP2) perturbation treatment. Within this MP2/6-31G* approach, geometry optimization and harmonic vibrational analysis were performed for selected structural types.…”

“…In fact, the small clusters had been studied well before fullerene discovery [5], by both computational [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and experimental [-22-41] means. C 9 belongs to the species for which at least fragments of information are available from experiment [42].…”

Double Aromaticity in Monocyclic Carbon, Boron, and Borocarbon Rings Based on Magnetic Criteria

“…[74] Alternatively, Slanina et al identified a boatlike nonplanar D 4d structure as a minimum. [146,147] The energy difference between these two structures, less than 1 kcal mol À1 at the B3LYP/aug-cc-PVTZ level, [67] again reflects the fluxional character of these systems. Both the C 4h and D 4d minima have small HOMO-LUMO gaps (only 1.21 eV at PW91/IGLO-III//B3LYP/6- Figure 6.…”