Butane hydrophobic effect

Using the data given in Section 3.2.5, and a 40 cal / mol A value for the hydrophobic effect, calculate the difference in surface area for anti and gauche butane. Given an estimated surface area for anti butane of 127 A estimate the surface area of gauche butane. 

Table 2.1 Change in standard molar Gibbs energy, enthalpy and entropy (all in kj mot ) for the transfer of hydrocarbons from pure liquids into water at 25 °C (Prausnitz, Lichtenthaler and de Azevedo, 1999 Gill and Wadso, 1976). Notice the large negative entropy changes due to the hydrophobic effect, in the case of n-butane, the entropy decrease amounts to 85% of the Gibbs energy of solubilization, while for other hydrocarbons the entropic contribution is even larger...

In 1959, Kauzmann indicated the effects of nonpolar groups on the structure of water, the so-called hydrophobic effects in stabilizing protein structures. Wish-nia examined the solubility of ethane, propane, and n-butane in aqueous solutions of bovine serum albumin (BSA), hemoglobin (Hb), lysozyme, and sodium lauryl sulfate (SLS). 

For polar organic substances more soluble in water than in organic liquids, there will be little movement if an anhydrous mobile phase is used adding water to the solvent will cause those substances to migrate. Thus, butan-1-ol is not a suitable solvent for amino acids unless it is saturated with water addition of acetic acid allows more water to be incorporated, and hence increases the solubility of amino acids, particularly basic ones the addition of ammonia increases the solubility of acidic materials. tert-Butanol and water mixtures are the primary solvent for the separation of many polar anionic species, and many other polar substances with solubility characteristics similar to those of amino acids, such as indoles, guanidines and phenols, can be separated with this mixture. For hydrophobic stationary phases, various mixtures of benzene, cyclohexane and chloroform have been used to good effect as eluants. 

That the concept of hydrophobic bonding does not square with the facts, is pointed out by Hildebrand (1979) who maintained that the very concept of a hvdrophobic effect is unreal. No hydrophobic substance has yet been discovered every substance is hydrophilic, although hydrocarbons are very little so. In support of the hydrophilicity of hydrocarbons, Hildebrand instanced that the energy required to evaporate a mole of butane from its aqueous solution (at 1 atm and 25°C) is 0.65 kcal greater than from its own pure liquid. He also pointed out that if you pour some octane on ice, you can see that the ice is instantly wet by it (Hildebrand, 1979). 

Another prototypical system is the trans/gauche equilibrium for butane, which has been addressed by numerous pmf determinations. There is uniform agreement with integral equation theories that there is an increase in the gauche population of ca. 15% in water over the gas phase owing to hydrophobic preference for the more compact conformer. This is not a general packing effect since such shifts are absent in nonpolar solvents and in neat alkane liquids. ... 

---