text: The most common types of π-interactions involve: 
  *Metal–π interactions: involves interaction of a metal and the face of a π system, the metal can be a cation (known as cation–π interactions) or neutral
  *Polar–π interactions: involves interaction of a polar molecule and quadrupole moment a π system.
  *Aromatic–aromatic interactions (π stacking): involves interactions of aromatic molecules with each other.
  **Arene–perfluoroarene interaction: electron-rich benzene ring interacts with electron-poor hexafluorobenzene.
  *π donor–acceptor interactions: interaction between low energy empty orbital (acceptor) and a high-energy filled orbital (donor).
  *Anion–π interactions: interaction of anion with π system
  *Cation–π interactions: interaction of a cation with a π system
  *C–H–π interactions: interaction of C-H with π system: These interactions are well studied using experimental as well as computational techniques.