The Chemical Bond
Functional Groups in Organic Chemistry
|Intermolecular forces are electrostatic interactions that operate between molecules. They are of primarilly three types: dipole-dipole, hydrogen bonding, and Van der Waals (or London disperson forces). The type of intermolecular force a molecule exert depends on the electronegativity difference between its bonded atoms and its molecular geometry. Polar covalent bonds make it possible for a molecule to engage in dipole-dipole interactions.|
Furthermore, in the special case where a hydrogen atom is covalently bonded to a highly electronegative atom such as nitrogen or oxygen, the type of intermolecular force that results is called hydrogen bonding. Because the hydrogen end is a bare proton that can partially share electrons from the negative pole of the adjacent molecule, hydrogen bonds are an order of magnitude stronger than ordinary dipole-dipole interactions. Lastly, nonpolar molecules interact by London dispersion forces, which are weaker than dipole-dipole interactions or hydrogen bonds.
It is especially essential when you go into the MCAT to have good sense of the types of intermolecular forces exerted by the organic functional groups. Intermolecular force is a major conceptual foundation for understanding many phenomena including the physical properties and solution properties of substances.