Möbius bis and tris-spiroaromatic systems

Abstract

We propose that a general class of bis and tris-spiro 7-membered ring systems with a common atom X, of which there are a number of examples characterised crystallographically, can in fact be considered as spiroaromatic molecules in which each ring exhibits some degree of Möbius 4nπ-electron aromaticity. The aromaticity is probed as a function of the spiro-atom using ab initio calculations of the NICS(0) values, which indicate that the Möbius-aromaticity increases as the spiro-atom is changed e.g. from Al to P, and from e.g. P to As.