Bowl stacking in curved polynuclear aromatic hydrocarbons: crystal and molecular structure of cyclopentacorannulene

Abstract

Cyclopentacorannulene (dibenzo[ghi,mno]cyclopenta[ cdlfluoranthene) exhi bits long-range concave-convex bowl stacking in the crystal; its molecular structure is satisfactorily described b y a6 initio calculations at both HF/3-21 G and HF/6-31 G* levels.The discovery of the fullerenesl has prompted a general interest in bowl-shaped aromatic hydrocarbons whose carbon frameworks are represented on the buckminsterfullerene surface. The first known and simplest example is corannulene2 (C20H10, 1) whose carbon framework represents the polar cap of buckminsterfullerene. Of course an exciting feature of curved hydrocarbons is their bowl shape, and this leads to the interesting question about their potential for complexation in a convedconcave relationship. This latter type of stacking might be expected for the minimum energy arrangement of two bowl-shaped molecules since it maximizes attractive van der Waals interactions. Moreover, in addition to the interaction of two bowl-shaped compounds, such a relationship could also occur between bowl-shaped hydrocarbons and spherical molecules of roughly the same curvature: e.g. buckminsterfullerene or other fullerenes.Bowl-shaped corannulene undergoes rapid bowl-to-bowl inversion in solution,3 and X-ray analysis shows4 several different relative orientations of two molecules of 1 with very little bowl stacking. 1-Thus, even though such concave-convex interactions have been observed in the gas phase between corannulene and the corannulene radical cation 2, and between corannulene and buckminsterfullerene radical cation 3,5 there has been no evidence to suggest the importance of such relationships in either solution or in the solid state.In contrast to corannulene itself, cyclopentacorannulenes 4 and 5 are presumed to be 'locked' into the bowl shape, at least on the NMR timescale, since the endo and e m benzylic protons of 4 remain distinct, even at elevated temperatures.6 We now provide molecular and crystal structure data for cyclopentacorannulene 5 showing that the additional fivemembered ring not only generates considerably more curvature, but also leads to 'bowl stacking' in the crystal, an arrangement absent in corannulene itself.

Cycloaromatization of Open and Masked 1,3-Hexadien-5-ynes − Mechanistic and Synthetic Aspects

“…Only the FP of [4-D]-1-phenyl-1-buten-3-yne (50) shed any more light on this process (Scheme 12). [8] The formation of about 13% of 47 clearly indicates operation of the type C mechanism, but the monodeuterated naphthalenes 51 and 52 that were also detected are also partially formed by this mechanism, although not in a higher percentage than 47 (for more details, see ref.…”

π-Conjugated Anions: From Carbon-Rich Anions to Charged Carbon Allotropes

“…The additional five-membered ring in 9 leads to a significant increase in curvature relative to 5. [41] The potential energies [11] for the LUMOs of 8 and 9 (semiempirical AM1 calculations) are calculated to be -1.180 eV and -1.558 eV, respectively, even lower than in the case of 5 (-1.028 eV). In 8 and 9, as in 5, the LUMO is nondegenerate, but there is only a small energy gap between the LUMO and the NLUMO (0.22 eV and 0.62 eV, respectively), which thus allows the formation of highly reduced species.…”

Synthesis, Structures, and Physical Properties of Aromatic Molecular-Bowl Hydrocarbons

“…Based on the crystallographic analysis, both the bowl depth (ca. 1.05 Å) [112] and the POAV pyramidalization angles (10.7 , 9.7 , and 9.0 ) for the hub ring in 67 are larger than those for the parent compound 1.…”