Water as Solvent and Reactant

Water is an angular molecule with an H-O-H bond angle of 104.5° and an O-H bond length of 0.96 A. The energy of dissociation of the O-H bond is about 450 kJ/ mol, much higher than that for typical C-C bonds which average around 350 kJ/ mol. 

Water has a very high latent heat of vaporization (2300 J/g, by far the highest of all common liquids), and accordingly, considerable energy must be supplied to the liquid to convert it to the vapor. Nevertheless, the atmosphere always contains water both in the vapor state and in the form of small aerosol droplets. At 20°C, up to 17 g water vapor/m can be held in the air. 

Liquid water. The structure of liquid water is still controversial. Some models suggest that it can be represented as a slightly disordered ice, although these representations do not account very well for the remarkable degree of supercooling (up to 40°C) that the liquid can exhibit. It would be expected that ice-like assemblages would be efficient nuclei for crystallization. 

Aromatic hydrocarbons also decrease in solubility with size, although they are far more soluble (approximately two orders of magnitude on a molar basis) than aliphatic hydrocarbons having the same number of carbon atoms (Mackay and Shiu, 1977 Pearlman et al., 1984). The solubilities of benzene, toluene, and naphthalene are, respectively, 1750 mg/L (0.022 M), 550 mg/L (6 x 10 M), and 32 mg/L (2.5x10 M). Even a rather large aromatic compound such as phenanthrene (C Hio) has a solubility of nearly 1/tM. It is probable that there are significant charge-transfer interactions between water molecules and the pi electron clouds of aromatic species. 

Striking increases in water solubility result when heteroatoms are introduced into hydrocarbon chains, due to the ability of the substituent to take part in hydrogen bonding and assume a position in the structural framework of the liquid. The solubility of -hexane is only about 1 x 10 M, but that of di-n-propyl ether is about 

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