Electron-counting rules, three-dimensional aromaticity, and the boundaries of the Periodic Table

Abstract

To describe aromaticity of planar and three-dimensional molecules, different electron counting rules are employed. Here, the relationship between the Huckel 4n + 2 rule and the Hirsch 2(n + 1)2 rule is established based on formal approach considering the electrons as objects in an arbitrary n-dimensional space of states. Two types of three-dimensional aromaticity, referred to as ‘spherical’ (following the 4n + 2 electron counting rule) and ‘spatial’ (following the 2(n + 1)2 electron counting rule) are distinguished. A conclusion concerning the boundaries of the Periodic Table of Elements is made based on the same formal approach that no g- (or higher) elements can exist and that possible extension of the Periodic Table beyond the seventh period must be followed by filling of the 8p or inner 6f or 7d levels. Copyright © 2011 John Wiley & Sons, Ltd.