Water molecules hydrogen bonding cooperativity

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... 

The remarkable protonation features of 21 led to the formulation of the diproto-nated species as the water cryptate, [H20 cr 21, 2H+] 25, in which the water molecule accepts two +N-H---0 bonds from the protonated nitrogens and donates two 0-H---N bonds to the unprotonated ones [2.17, 2.96], The second protonation of 21 is facilitated by the substrate it represents a positive cooperativity effect, mediated by H20, in which the first proton and the effector molecule water set the stage both structurally and energetically for the fixation of a second proton. When 21 is tetraprotonated it forms the chloride cryptate cryptate [Cl c 21,4H+] 26, in which the included anion is bound by four +N-H---X- hydrogen bonds [2.97] (see also Chapt. 3). 

Thus, specific interactions directly determine the spectroscopic features due to hydrogen bonding of the water molecules, while unspecific interactions arise in all or many polar liquids and are not directly related to the H-bonds. Now it became clear that the basis of four different processes (terms) used in Ref. [17] and mentioned above could rationally be explained on a molecular basis. One may say that specific interactions are more or less cooperative in their nature. They reveal some features of a solid state, while unspecific interactions could be understood in terms of a liquid state of matter, if we consider chaotic gas-like motions of a single polar molecule, namely, rotational motions of a dipole in a dense surroundings of other molecules. The modem aspect of the spectroscopic studies leads us to a conclusion that both gas-like and solid-state-like effects are the characteristic features of water. In this section we will first distinguish between the following two mechanisms of dielectric relaxation ... 

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