No abstract

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

No 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.

No abstract