page_title: Non-covalent interaction
section_title: Cation–π and anion–π interaction
hierarchical_section_title: Non-covalent interaction / π-effects / Cation–π and anion–π interaction
caption_attribution_description: English: Sodium cation sitting atop the pi system of a benzene ring through a cation-pi interaction.
context_page_description: A non-covalent interaction differs from a covalent bond in that it does not involve the sharing of electrons, but rather involves more dispersed variations of electromagnetic interactions between molecules or within a molecule. The chemical energy released in the formation of non-covalent interactions is typically on the order of 1–5 kcal/mol. Non-covalent interactions can be classified into different categories, such as electrostatic, π-effects, van der Waals forces, and hydrophobic effects.
  Non-covalent interactions are critical in maintaining the three-dimensional structure of large molecules, such as proteins and nucleic acids. In addition, they are also involved in many biological processes in which large molecules bind specifically but transiently to one another. These interactions also heavily influence drug design, crystallinity and design of materials, particularly for self-assembly, and, in general, the synthesis of many organic molecules.
  Intermolecular forces are non-covalent interactions that occur between different molecules, rather than between different atoms of the same molecule.
context_section_description: Cation–pi interactions involve the positive charge of a cation interacting with the electrons in a π-system of a molecule. This interaction is surprisingly strong (as strong or stronger than H-bonding in some contexts), and has many potential applications in chemical sensors. For example, the sodium ion can easily sit atop the π cloud of a benzene molecule, with C₆ symmetry (See figure 4).
  Anion–π interactions are very similar to cation–π interactions, but reversed. In this case, an anion sits atop an electron-poor π-system, usually established by the placement of electron-withdrawing substituents on the conjugated molecule
caption: Figure 4
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