Hydrogen bonding in water

Milet A, Moszynski R, Wormer P E S and van der Avoird A 1999 Hydrogen bonding in water olusters pair and many-body interaotions from symmetry-adapted perturbation theory J. Phys. Chem. A 103 6811-19... 

Figure C2.14.2. The hydrogen bond in water. The oxygen lone pairs (shaded blobs) are the donors, and the hydrogen atoms the acceptors [ 177, 178].

Hydrogen bonding in water is cooperative. That is, an H-bonded water molecule serving as an acceptor is a better H-bond donor than an unbonded molecule (and an HgO molecule serving as an H-bond donor becomes a better H-bond acceptor). Thus, participation in H bonding by HgO molecules is a phenomenon of mutual reinforcement. The H bonds between neighboring molecules are weak (23 kj/mol each) relative to the H—O covalent bonds (420 kj/mol). As a consequence, the hydrogen atoms are situated asymmetrically... 

To make it more meaningful, let s take the reaction for the formation of a hydrogen bond in water ... 

The presence of hydrogen bonding in water is shown by its anomalous thermophysical properties and has been confirmed by more recent methods of investigating its structure such as NMR, neutron scattering, dielectric relaxation, ultrasonic absorption,... 

Schuster, P. Theory of hydrogen bonding in water and ionic solutions. In Structure of water and aqueous solutions (Proceedings of the International Symposium, Marburg 1973), p. 142 (W. A. P. Luck, ed.). Weinheim Verlag Chemie 1974. 

In equation 8.5, is the constant of distortion of the hydrogen bond. The degree of distortion of the hydrogen bond in water varies with temperature [from 26° to 30° for 0 < r(°c) < 100] and is zero in ice, where H2O molecules are linked to form perfect tetrahedra. 

We know that there are also hydrogen bonds in water. It is these hydrogen bonds which make water a unique liquid, very different from other liquids even those which have a similar chemical structure. The hydrogen bond between hydrogen atoms in different molecules, is approximately 10 times weaker than the covalent bond. But we really operate with these bonds when we break liquid water into cold mist This has led me to the conclusion that the hydrogen-hydrogen bonds are somehow connected with excess energy release. 

Second, rate constants for intermolecular proton transfer obey the Brpnsted relationship, and the rates can be strongly influenced by electrostatics as well as the difference in the p/ a s for the two acids. Third, proton transfer can proceed at slower than diffusion-limited values with compounds forming weak hydrogen bonds in water. 

Kato Y, Conn MM, Rebek J. Hydrogen-bonding in water using synthetic receptors. Ptoc Natl Acad Sci USA 1995 92 1208-1212. 

Hydrogen bonding in water. Hydrogen bonds are represented by dashed lines. Only several water molecules are shown and not all bonds are displayed. The pattern for the central oxygen atom continues to form a network of hydrogen-bonded water molecules. 

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