Classification of Solvents according to Chemical Constitution

Solvents can be classified according to their chemical bonds (a) molecular liquids (molecule melts covalent bonds only), (b) ionic liquids (molten salts only ionic bonds), and (c) atomic liquids (low-melting metals like liquid mercury or liquid sodium metallic bonds) [16]. Numerous transitions are possible by mixing solvents of these three classes (Fig. 3-1). However, research into this area is still far from exhausted. 

Further well-known molecular liquids that have recently found renewed interest as solvents for many applications are water and perfluorohydrocarbons. These occupy the two extreme positions on empirical solvent polarity scales, with water being the most polar solvent and perfluorohydrocarbons being among the least polar of solvents cf. Chapter 7). 

Plain water has undergone a magnificent renaissance as a solvent for organic reactions, not only because it is an environmentally safe solvent, but also due to its pronounced capacity for hydrophobic hydration of apolar solutes [178-181] cf. Sections 2.2.7 and 5.5.8 as well as Table A-14 in the Appendix. 

Solvents and Solvent Effects in Organic Chemistry, Third Edition. Christian Reidiardt Copyright 2003 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-30618-8 

Liquid erystals or mesomorphie eompounds oeeupy a special position [17-22, 22a, 109, 110]. Compounds capable of forming liquid erystals are long, flat, and fairly rigid along the axis of the moleeule. Most known mesomorphic solvents are systems of the following general structure with polarizable aromatic nuclei held in a planar skeleton  

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