Preference for Na+-pi binding over Na+-dipole binding in Na+-arene interactions.

The cation binding of dipolar aromatics was investigated employing computational techniques. In most cases, cation binding at the pi region of the aromatic (the cation-pi interaction), which can be thought of as a cation-quadrupole interaction, is preferred over cation binding at the negative end of the dipole moment. Surprisingly, in some cases, the cation-dipole complex is not even a minimum on the potential energy surface.