Hydrogen bonding condensed phases

The hydrogen atom has a high ionization energy (1312kJmol ) and in this it resembles the halogens rather than the alkali metals. Removal of the Is electron leaves a bare proton which, having a radius of only about 1.5 x 10 pm, is not a stable chemical entity in the condensed phase. However, when bonded to other species it is well known in solution and in... 

As discussed in Chapter 6, water forms strong hydrogen bonds and these lead to a number of important features of its atmospheric behavior. All three phases of water exist in the atmosphere, and the condensed phases can exist in equilibrium with the gas phase. The equilibria between these phases is summarized by the phase diagram for water. Fig. 7-9. 

Theoretically, the problem has been attacked by various approaches and on different levels. Simple derivations are connected with the theory of extrathermodynamic relationships and consider a single and simple mechanism of interaction to be a sufficient condition (2, 120). Alternative simple derivations depend on a plurality of mechanisms (4, 121, 122) or a complex mechanism of so called cooperative processes (113), or a particular form of temperature dependence (123). Fundamental studies in the framework of statistical mechanics have been done by Riietschi (96), Ritchie and Sager (124), and Thorn (125). Theories of more limited range of application have been advanced for heterogeneous catalysis (4, 5, 46-48, 122) and for solution enthalpies and entropies (126). However, most theories are concerned with reactions in the condensed phase (6, 127) and assume the controlling factors to be solvent effects (13, 21, 56, 109, 116, 128-130), hydrogen bonding (131), steric (13, 116, 132) and electrostatic (37, 133) effects, and the tunnel effect (4,... 

Glycerol is well known for its strong hydrogen bonding in the liquid phase and its high viscosity. To study its wetting properties, we deposited glycerol on mica by condensation from its vapor in standard laboratory air [9]. 

Elsaesser TH, Bakker HJ (2002) Ultrafast hydrogen bonding dynamics and proton transfer processes in the condensed phase. Springer, Heidelberg... 

On Pt(lll) the HREELS features due to water are unchanged by the presence of CO. These observations indicate that water and CO adsorb onto separate patches on the surface, in a form of hydrophobic coadsorption. Water condenses into hydrogen-bonded islands, as indicated by the low 0-H stretching frequency. CO spreads to cover the rest of surface, giving a phase similar to that for CO alone, but with a coverage normalized to the water-free, not total, surface area. COCO repulsions, which have been well documented on Pt(lll) (10), produce a surface pressure within the CO patches which bears upon the edges of the water islands. It is this lateral pressure which causes water to desorb from Pt(lll) at lower temperatures in the presence of coadsorbed CO. 

Aromaticity varies with change of state because of the influence of the molecular environment on the interactions that determine aromaticity quantitatively, particularly in nonsymmetrical heterocycles. Comparative calculations of aromaticity indices for molecules in the gas phase and in condensed media with dielectric constants > 1, with or without hydrogen-bonding, showed coherent results for a set of nitrogen heterocycles, including imidazole, pyrrole, pyrazole, 1//-1,2,4-triazole, and benzimidazole. The... 

In conclusion, lifetimes and quantum yields are characteristics of major importance. Obviously, the larger the fluorescence quantum yield, the easier it is to observe a fluorescent compound, especially a fluorescent probe. It should be emphasized that, in the condensed phase, many parameters can affect the quantum yields and lifetimes temperature, pH, polarity, viscosity, hydrogen bonding, presence of quenchers, etc. Attention should be paid to possible erroneous interpretation arising from the simultaneous effects of several factors (for instance, changes in viscosity due to a variation in temperature). 

It is instructive to illustrate the use of Equations 5.19 and 5.29 using a simplistic 3-atom model calculation for water. Even though it is well established that the condensed phase structure of water is complicated and involves the coordinated motions of many molecules coupled through a constantly fluctuating hydrogen bond network, the fundamentals of the VPIE are represented reasonably well by the simplified model. 

For gas-phase ir studies, it has been possible to show good correlation between Av h and (AHB) (Millen et ai, 1979). Even with condensed phases, this method is still fairly reliable, e.g. with alcohols (Piaggio et ai, 1983), and Av-AH correlations have recently been shown to hold for hydrogen-bonded ions (McMahon and Larson, 1984b). 

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