Cation–π interactions arise from an electrostatic interaction between a positively charged ion and the partial negative on the face of an aromatic ring, which results from the quadrupole moment of the aromatic ring (Figure 7.1).¹  This quadrupole moment arises from the difference in electronegativity of the sp²-hybridized carbons and hydrogens in the aromatic ring. While these interactions are often seen with aromatic rings, it should be noted that the aromaticity is not a necessity for this interaction, rather just the Coulombic interaction between a partial negative π surface and a cation is necessary.³ 

Computational...