Hydrogen bonding in liquids and

Q From the (.lata given in Table 1.1, what evidence is there for hydrogen bonding in liquid and solid water. ... 

R. Ludwig, F. Weinhold, and T. C. Farrar. Theoretical study of hydrogen bonding in liquid and gaseous A-methylformamide. J. Chem. Phys. 107, 499-507 (1997). 

Study of Hydrogen Bonding in Liquid and Gaseous N-Methylformamide. 

Proton (1H) NMR has proved to be a sensitive method for studying hydrogen bonding in liquids and electrolyte solutions (6,7). Formation of a hydrogen bond causes the resonance of the bonded proton to move downfield. Hence, an upheld shift can be correlated with the breaking up of hydrogen bonds. This behavior has led to the characterization of ions in terms of their effect on water structure (7). 

Figure 11. Average parameters of hydrogen bonds in liquid and supercritical water.

However, by far the most common non-covalent interaction responsible for generating new liquid-crystalline species is the hydrogen bond, and this area has been well reviewed [ 16,17]. In fact, hydrogen bonding in liquid crystals is a very old concept and it has been known for some time that, for example, the... 

Studies have indicated that the association of HF in the gas phase leads predominantly to dimers or hexamers with small amounts of tetramers. Hydrogen bonding in liquids such as sulfuric and phosphoric acids is responsible for them being viscous liquids that have high boiling points. 

In many of its properties, liquid ammonia resembles water. Both are polar and involve extensive hydrogen bonding in the liquid state. It is interesting to note that hydrogen bonding in liquid... 

Finally, as a simple illustration of how weak these forces are, note how the energy required to break the hydrogen bonds in liquid hydrogen chloride (i.e. the energy required to vaporize it) is 16 kJmol-1, yet the energy needed break the chemical bond between atoms of hydrogen and chlorine in H-Cl is almost 30 times stronger, at 431 kJmol-1. 

VIBRATIONAL LINE SHAPES, SPECTRAL DIFFUSION, AND HYDROGEN BONDING IN LIQUID WATER... 

Hydrogen bonding in liquid water was discussed. The significance of the dipolar character of the water molecule was pointed out and its relation to the large value of the permittivity of the bulk... 

The role of hydrogen bonds in liquid or vapour-phase adsorption processes has not hitherto been very clearly defined. The present paper is a brief review of some recent investigations in this laboratory, many of them unpublished, which it is believed may help to define the conditions favouring hydrogen bond adsorption especially from dilute solutions, by inorganic and organic substrates. 

The hydrogen bonds in crystalline and liquid ammonia are weaker than those in ice and water for two reasons the small ionic character of the N—H bond gives it only small hydrogen-bond-forming power, and the one unshared electron pair of the NH8 molecule must serve for... 

Consequently, vibrational spectra, and, particularly, Raman data on the shape, the intensity, and the frequency of OH bands, should be helpful in the elucidation of weak-energy hydrogen-bonds in liquids.217... 

Complete ionization of a hydrogen atom is possible in the gas phase, where the hydrogen ion is present as a bare proton of radius 1.5 X 10 3 pm, about 100,000 times smaller than the radius of a hydrogen atom. In liquids and solids, however, the bare proton is too reactive to exist by itself. Instead, the proton bonds to a molecule that has a lone pair of electrons. In water, for example, the proton bonds to an H20 molecule to give a hydronium ion, H30 + (aq). 

At l(atm), Hr v should be negligible relative to AHlv. Then HRl —AHlv. Because the normal boiling point is a representative T for typical liquid behavior, and because HR reflects intermolecular forces, A Hlv has the stated feature. s.Hlv( CO) is much larger than A/Z ICIE) because of the strong hydrogen bonding in liquid water. 

Hydrogen Bonding in Liquid Water and Aqueous Solutions. 

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. 

The use of hydrogen bonds in liquid crystalUne materials at large is a very active area [63,64]. In the case of main chain thermotropic liquid crystalUne HBSPs, two main approaches have been explored. The first approach is to mix two complementary monomers, usually of the AA -i- BB type (Fig. 1). The complementary hydrogen bonding units utilized are mainly modified nu-cleobases [5,65,66] and aromatic acid/pyridine couples [54,67- 74]. In the most successful cases, the pure components are not mesomorphous, but the mixtures are [65,69-71]. At any rate, the stabiUty range of the mesophase is usually increased. The second approach is to use a self-complementary... 

In liquid hydrazine, hydrogen bonding occurs between the hydrazine molecules similar to the hydrogen bonding in liquid water. In solid hydrazine, the hydrogen bonds have NH-N distances between 319 and 367 pm. In hydrazine hydrate, each hydrazine molecule is linked via six hydrogen bonds to surrounding water molecules so that the hydrazine molecules are separated from each other by water molecules. Some physical properties of hydrazine and hydrazine hydrate are shown in Table 16. 

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