Interactions Involving Polar Molecules

This chapter explores the interactions that involve polar molecules. Dipolar or polar molecules are the molecules that posses an electric dipole. The dipoles of some molecules depend on their environment and can change substantially when they are transferred from one medium to another, especially when molecules become ionized in a solvent. When two polar molecules are near each other, there is a dipole–dipole interaction between them that is analogous to that between two magnets. Polarity can also arise from internal charge displacements within a molecule, producing zwitterionic molecules or groups. In larger molecules, or “macromolecules,” such as proteins, the net dipole moment is usually made up of a distribution of positive and negative charges at various locations of the molecules. The chapter discusses electrostatic pair interaction between a charged atom and a polar molecule. The chapter explains strong ion–dipole interactions in water. The solvation forces, structural forces, and hydration forces are also explained. The chapter concludes with a discussion on dipole–dipole interactions.