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Figure 1
The quadrupolar model of stacking of aromatic rings proposed by Hunter & Sanders (1990BB35). Energetically favourable arrangements of the rings are (a) parallel and offset or (b) T-shaped. The face-to-face arrangement shown in panel (c) is energetically unfavourable due to strong repulsion between the π-electron clouds. The typical geometry for type (a) is a centroid-to-centroid distance >3.8 Å, an interplanar distance >3.5 Å and an offset of ca 1.7 Å.

IUCrJ
Volume 6| Part 2| March 2019| Pages 156-166
ISSN: 2052-2525
https://doi.org/10.1107/S2052252519000186