Iceberg structure

Hydrophobic effect — Effect that nonpolar compounds possess a low solubility in water. The reason for the low solubility is that nonpolar compounds when they dissolve in water destroy the water structure (hydrogen bonds) because of cavity formation, what is accompanied by a loss of entropy, and the water molecules are forced to order around the solute molecule ( iceberg structure), which is a further loss of entropy. These entropy losses are not compensated for by formation of strong bonds between the solute and water, as it happens in case of polar molecules or esp. in case of ions. 

The unusual thermodynamic properties of nonpolar solutes in aqueous phase were analyzed, by assuming that water molecules exhibit a special ordering around the solute. This water-ordered structure was called the iceberg structure. 

The driving force for the association of hydrocarbon chains into a micellar core is an increase in the entropy of the system, which occurs primarily due to destruction of iceberg structure present in water. Such structures are present around the hydrocarbon chains of dissolved surfactant molecules. 

It is now recognized that, when hydrocarbon molecules are dissolved in water, a structure like an iceberg may be formed around the solute molecules[l]. The structure resembles that of a gas hydrate where the gas molecule is encaged in a nearly spherical space formed by hydrogen bonded water molecules. Structures of various gas hydrates have so far been extensively investigated with X-ray diffraction techniques[2-U], but a study of the iceberg structures formed in solution is very difficult because of quite low solubilities of hydrocarbons in water. 

In this study, we succeeded in the observation of Raman spectra of benzene, cyclohexane and chloroform in aqueous solution. These molecules are known to form hydrate clathrates of type M 1TH20[2], and were selected because of their high solubilities in water, relative to other saturated hydrocarbons, and because of their strong Raman lines. It may be expected that the iceberg structure formed around the solute in aqueous solution affects the rotational motion of the solute molecule. Thus the rotational diffusion constants have been determined from the linewidths of the isotropic and anisotropic Raman spectra, and the effect of the iceberg structures on the rotational motion of the solute molecules is discussed from a comparison of the rotational diffusion constants in various solutions. 

The model of the ring of six water molecules which you showed surrounding a hydrocarbon chain is very similar to a six membered ring occurring in the crystal structure of ice. It appears that your proposed complex is not different from the clathrate or iceberg structures proposed quite some time ago to explain hydrocarbon-water interactions. 

For a compound i, the partition coefficient is defined as Pi = ai(o)lai(w), where af(o) and a/(w) stand for the activities of the compound i in octan-l-ol and water, respectively. In general, the more positive value of log(P), measured in the biphasic system of octan-l-ol/water, means the higher lipophilicity of the investigated system. See also hydrophobic effect, and iceberg structure. 

A table of ion mobilities is given below (Table 4.3). It is seen that and OH ions in aqueous solution are exceptional in having extremely high mobilities. In view of what has become known about the extent of association of water molecules ( iceberg structures) in recent years, such large values cannot... 

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