Chapter 5 - Intermolecular Interactions

Abstract

Interaction energy of molecules may be calculated by subtracting the subsystems' energies from the total system energy (supermolecular method). The method works independently of the interaction strength. There are some disadvantages though: a loss of accuracy and a lack of information about physical components of the interaction energy. The alternative perturbational method requires long- or medium-range intermolecular distances. Its most important contributions, electrostatic, valence repulsion, induction, and dispersion, lead to a richness of supramolecular structures. The hydrogen bond X–H⋯Y represents an example of domination of the electrostatic interaction. The all important valence repulsion controls how the interacting molecules fit together in space. In aqueous solutions the solvent structure contributes very strongly, leading to what is known as the hydrophobic effect – expulsion of the nonpolar subsystems from the bulk, which looks like their attraction. A precise molecular recognition may be planned by chemists helping to build complex molecular architectures by molecular self-organization.