Hydrogen bonding, between water and

FIGURE 24.1 (a) A hydrogen bond between two phenol molecules (b) hydrogen bonds between water and phenol molecules. 

Figure 3.14 The full line and circles show the hnear relation between oh- and Fq for OH adsorbed alone on the surface in the most stable site. The dashed line and crosses represent the same relationship, but calculated for OH in the OH/H2O layer. The downward shift is related to hydrogen bonding between water and OH. Another important effect is that the deviation from the line is much smaller in the OH/H2O layer. The correlation coefficient is improved from = 0.92 to 0.97 by including the water. This is partly because in the OH/H2O layer all metals binds OH on top. The figure is based on data from [Karlberg, 2006].

Hydrogen bonding between water and polar solutes also causes some ordering of water molecules, but the effect is less significant than with nonpolar solutes. Part... 

The hydrogen bonds in liquid water have an average lifetime of less than 10"10 second as measured by dielectric relaxation times (4). But the hydrogen bonds between water and a polymer could exist for longer than 10"7 seconds. Such a structure would appear permanent at the frequencies used in the ultrasonic impedometer (107 cycles/sec. range), and should demonstrate a measurable shear stiffness at these frequencies. 

In contrast, the highly polar organic compound methanol, CH3OH, is quite soluble in water. Hydrogen bonds between water and methanol molecules can readily replace the very similar hydrogen bonds between different methanol molecules and different water molecules. 

FIGURE 1.5 Hydrogen bonding between water and (a) hydroxyl groups, (b) keto groups (c) carboxyl groups and (d) amino groups. 

Another important issue of ethanol is its water sensitivity, which affects the water tolerance of gasoline in the case ofwater presence in ethanol-added gasoline, there is, in fact, the formation of hydrogen bonds between water and alcohol and the blend separates into two phases, with loss of octane quality. As a consequence, bioethanol requires special handling with different storage and distribution facilities for alcohol and gasoline and the blend has to be carried out just before the final use. 

Polyethylene oxide) and poly(N-alkylacrylamide)s are known to undergo a temperature-dependent phase change whereupon they separate from an aqueous phase at increased temperatures [14]. This inverse temperature dependence, i.e., the occurrence of a lower critical solution temperature, can be related to an entropi-cally favorable decrease in hydrogen bonding between water and the polymer with increasing temperature. In order to exploit this physical property for catalyst recovery, Bergbreiter et al. attached phosphines covalently to commercially available PEO or PEO-b-PPO-b-PEO block copolymers [Schemes 1 and 2 PPO = polypropylene oxide)] [9a],... 

The reverse process, that is drying, is far much more difficult because of very strong hydrogen bonds between water and the fluoride anion, which is the smallest and the most electronegative halide. 

Fig. 4.4. Hydrogen bonds between water and polar molecules. R denotes additional atoms.

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