In chemistry, ion-association is a chemical reaction whereby ions of opposite electrical charge come together in solution to form a distinct chemical entity. Ion-associates are classified, according to the number of ions that associate with each other, as ion-pairs, ion-triplets, etc. Ion-pairs are also classified according to the nature of the interaction as contact, solvent-shared or solvent-separated. The most important factor to determine the extent of ion-association is the dielectric constant of the solvent. Ion-associates have been characterized by means of vibrational spectroscopy.