Effect of ring annelation on cations [M = H⁺, Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺]…benzene interaction: A density functional theory investigation

Density functional theory calculation was carried out on cation‐π complexes formed by cations [M = H + , Li + , Na + , K + , Be 2+ , Mg 2+ , and Ca 2+ ] and π systems of annelated benzene. The cation‐π bonding energy of Be 2+ or Mg 2+ with annelated benzene is very strong in comparison with the common cation‐π intermolecular interaction, and the bonding energies follow the order Be 2+ > Mg 2+ > Ca 2+ > Li + > Na + > K + . Similarly, the interaction energies follow the trend 1‐M < 2‐M < 3‐M for all the metal cations considered. These outcomes may be due to the weak interactions of the metal cations with CH and the interactions of metal cations with π in addition to the nature of a metal cation. We have also investigated on all the possible substituted sites, and find that the metal ion tends to interact with all ring atoms while proton prefers to bind covalently to one of the ring carbons. The binding of metal cations with annelated benzenes has striking effect on nuclear magnetic resonance chemical shifts using the gauge independent atomic orbital method.