Molecular Electrostatic Potential
Sigma-hole, Pi-hole and Molecular Electrostatic Potential (MESP) Sigma-hole is the positive electrostatic potential region of a molecule which is located at the outer extension of a sigma bond. For eg., the positive region of Cl-atom in the F3C-Cl molecule located at the outer periphery of C-Cl sigma bond. MESP of F3C-Cl molecule. Red region represents the sigma hole. Similarly, Pi-holes are defined as an extension of sigma-holes and are located at the pi-bonding region of a molecule. eg, NO2Br According to Politzer et.al, who proposed the concept of sigma-hole, when a half-filled p orbital on the halogen participates in forming a covalent bond, there results an electron deficiency in the outer (non-involved) lobe of that p orbital. This was called a σ-hole. What is the chemical origin of sigma-holes ? How one can correlate it with the molecular electron density ?