Criterion of H bonds

This sensitivity of the IR and Raman spectra for both gases and liquids was one of the earliest observations of the spectral uniqueness of H bonding systems. It has been used so frequently to verify the presence of H bonded species that many workers consider it to be the primary criterion of H bonding. Of much greater importance is the spectral measurement of equilibrium constants at several temperatures. Such data permit calculation of the thermodynamic properties of H bond formation, AH, AS, and AF (see Section 7.3.1)". ... 

The very large volume of research study of the IR and Raman spectra of H bonded substances is justified by the magnitude and the significance of the spectral perturbations. The most obvious importance of these changes, which are summarized in outline form in Section 3.1.3, has been repeatedly emphasized the spectral effects provide a criterion of H bonding which indicates specifically the role of the proton in the associative interaction. 

Crystallographic literature is full of information on the so-called close interatomic contacts, which in the case of distances between H-atoms and electron donating atoms are used as a criterion of H-bond existence. If this distance is shorter than the sum of van der Waals radii - then the H-bond type interaction is assumed... 

We use geometric criterion of H-bond existence [22]. According to it we assume that two water molecules are connected by H-bond if the distance between their oxygen atoms is not greater than R OOx and the distance between oxygen atom of first molecule and hydrogen atom of second molecule is not greater than R OHx, that is,... 

There is no universally accepted definition. Some definitions of the H bond are based on a single operational criterion (such as an infrared spectral shift), others on a listing of suitable functional groups, and still others on a mathematical or physical picture of H bond formation. We will use the term H bond to refer to an interaction that fits the following operational definition ... 

One of the interesting aspects of the correlation of v and Ava for the fundamental mode is its applicability to a wide variety of H bonded systems and its inapplicability to the m/ramolecularly H bonded compounds, salicylaldehyde and methylsalicylate (2054) (indicated in Fig. 3-13 by squares). The linear relation offers a critical test of theories of the band width, and possibly more experience will show that it is a criterion for distinguishing inter- and intramo tc x x H bonds. 

Lutski directed attention to the H bond in simpler molecules by proposing that the influence of ethanol solvent on the UV spectrum of an orthoh.y6.voxy keto- or nitro aromatic provides a criterion for an j n/ramolecular H bond (1287, 1285). Brieglieb and Strohmeier were able to detect the influence of H bonded dimer formation on the spectra of acetic acid vapor at different temperatures (near 2100 A) (279). There have followed many valuable studies directed at the effect of H bonding on the electronic transitions of acids such as phenols, aniline (1483, 1481, 2056), benzoic acid and derivatives (2076, 1998, 671, 190), acetanilides (2075, 2074), HF (1771, 1770), naphthols (1479, 1484), sulfinic acids (521), and amides (1436). The most extensive work, that of Nagakura, Baba, and co-workers, is of particular importance because it led to theoretical consideration of the nature of the H bond (see Section 8.3.2). (See adso 2056,. 1418, 1850.)... 

Guissani and Guillot 1993). At ambient conditions, this geometric criterion gives the average number of H-bonds per a water molecule (whb)g 3.2. 

Table 3. Average number of H-bonds per water moleeule and eoncentration of H-bonded speeies in supercritical BJH water at 630 K and 0.692 g/cm as a function of a lifetime criterion for H-bonds.

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