Topics - Hydrophobic
The word hydrophobic
has entered the terminology of chromatography largely from the fields of biology and biochemistry and, unfortunately as a result, has introduced some confusion into its exact meaning. Basically, in chromatography, the word is used as an alternative to dispersive
. Hydrophobic interactions are synonymous to dispersive interactions which are those resulting from London,s dispersion forces. Hydrocarbons, which are strongly dispersive in character and are in no way polar, do not mix with water because the dispersive interactive forces between hydrocarbon molecules themselves and the polar forces between water molecules themselves are very much greater than the dispersive forces between a water molecule and a hydrocarbon molecule. Water does not repel hydrocarbons, in fact, molecules can not repel one another (unless they are inside each others Van Der Waals radii). In addition, water has a finite, though small solubility in hydrocarbons and hydrocarbons have a small but finite solubility in water. This immiscibility of water and hydrocarbons is the basic source of the term hydrophobic
(fear of water). The term hydrophobic was originally used in biology and biochemistry to describe the overall property of a large molecule. If the substance, for instance, had a significant quantity of hydrocarbon chains in its molecule, then dispersive interactions would dominate over polar interactions when interacting with other molecules and the substance would be considered to be hydrophobic in character. The use of a term that was intended to describe the overall interactive properties of a molecule and to use it to describe a specific type of interactive force was not a good idea and has only resulted in many misunderstandings. Nevertheless, the term hydrophobic forces
persists and so in chromatography, hydrophobic forces should be interpreted as being synonymous with dispersive forces.