Entropy of hydrogen bonding

Equilibrium Constants, Enthalpies, and Entropies of Hydrogen Bonding of Hydroperoxides with Amides [30-32]... 

Actnally the differences between A S and ASq reflect largely the entropy of hydrogen bonding. However, the application of the eqns. [12.1.26] to [12.1.28] to room temperature data reveals, in eontrast to boiling point conditions, not unimportant contributions of S tt even for some aptotic hquids (see below). 

Solubility in Water A familiar physical property of alkanes is contained m the adage oil and water don t mix Alkanes—indeed all hydrocarbons—are virtually insoluble m water In order for a hydrocarbon to dissolve m water the framework of hydrogen bonds between water molecules would become more ordered m the region around each mole cule of the dissolved hydrocarbon This increase m order which corresponds to a decrease m entropy signals a process that can be favorable only if it is reasonably... 

Polyamides. The next two compounds are the amide counterparts of the esters listed under item (4). Although the values of AH j are less for the amides than for the esters, the values of T j, are considerably higher. This is a consequence of the very much lower values of AS j for the amides. These, in turn, are attributed to the low entropies of the amide in the liquid state owing to the effects of hydrogen bonding and chain stiffness arising from the contribution of the resonance form... 

The entropy value of gaseous HCl is a sum of contributions from the various transitions summarized in Table 4. Independent calculations based on the spectroscopic data of H Cl and H Cl separately, show the entropy of HCl at 298 K to be 186.686 and 187.372 J/(mol K) (44.619 and 44.783 cal/(mol K), respectively. The low temperature (rhombic) phase is ferroelectric (6). SoHd hydrogen chloride consists of hydrogen-bonded molecular crystals consisting of zigzag chains having an angle of 93.5° (6). Proton nmr studies at low temperatures have also shown the existence of a dimer (HC1)2 (7). 

Hydrophobic interactions of this kind have been assumed to originate because the attempt to dissolve the hydrocarbon component causes the development of cage structures of hydrogen-bonded water molecules around the non-polar solute. This increase in the regularity of the solvent would result in an overall reduction in entropy of the system, and therefore is not favoured. Hydrophobic effects of this kind are significant in solutions of all water-soluble polymers except poly(acrylic acid) and poly(acrylamide), where large heats of solution of the polar groups swamp the effect. 

Equilibrium Constants (K), Enthalpies (AH), and Entropies (AS) of Hydrogen Bonding of the Hydroperoxides ROOH + Y ROOH. .. Y... 

Hydroperoxides formed due to the oxidation of amides are decomposed into free radicals and accelerate oxidation. Hydroperoxides form hydrogen bonds with amides. The enthalpies, entropies, and equilibrium constants of hydrogen bonding are presented in Table 9.7. 

The number of hydrogen bonds per molecule in liquid water depends on the balance between the favorable energetic aspect of optimal hydrogen bonding and the unfavorable entropy considerations resulting from restrictions in water molecule location (Wallqvist and Mountain, 1999). 

Negative values for redox couple entropy have also been obtained for the Cu(II)/Cu(I) reduction, in aqueous medium, of the blue copper proteins stellacyanin, plastocyanin and azurin.14 The decrease in molecular disorder has been attributed in this case to the fact that the charge neutralization of the redox site (from + 1 to 0) favours the formation of hydrogen bonds between the solvent (water) and the copper centre.17... 

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