Hydrogen-bonding association model

This mechanism does not require a decision as to the question of whether the association of imidazole occurs through hydrogen bonding or by ionization. - However, if the methylation with diazomethane is considered together with methylations with dimethyl sulfate, dimethyl sulfate and alkali, and methyl iodide and the silver derivative of the imidazole, then such a comparison is best done using the hydrogen-bonded association model. 

C3+ complex cation always favors the homochiral combination (A-A or A-A) with the complex anion, while the C2 " complex cation always favors the heterochiral combination (A-A or A-A) with the complex anion. This tendency is explained by assuming that straight N-H--0 hydrogen bonds are formed in such a favorable pair. This hydrogen bonding association model has made possible the highly efficient optical resolution of electrically neutral tris(aminoacidato)cobalt( III). 

PVPh SMAc Styrene-methyl acrylate CP Carbonyl stretching bands shifts determined by FTIR used to correlate degree of hydrogen bonding association model applied to predict window of miscibility for the PVPh/SMAc blend 303... 

The OH group of phenol participates in two additional modes, in-plane and out-ofplane bending vibrations. The latter is also called the torsional mode toe observed near 300 cm (see Table 8) in the IR spectra of phenol vapour and of dilute solutions of phenol in w-hexane. In the associated molecules, it appears as a rather broad featureless band in the region of 600-740 cm ". It results from the hydrogen-bonded association. The spectra of liquid and solid phenol-OD also exhibit a variety of broad bands near 500 cm . The first overtone of the ton was found at 583 cm in the IR spectrum of phenol vapour. This assignment of the torsional mode allows one to model the torsional motion of the OH group of phenol by assuming that it is described by the... 

Deviations of real molecules from the reference system may occur, e.g., due to attractive interactions (dispersion), formation of hydrogen bonds (association), or the nonspherical shape of the molecules (which can be understood as the formation of chains from spherical segments). These contributions are usually assumed to be independent of each other and are accounted for by different perturbation terms. Depending on the kind of considered perturbation and on the expression used for its description, different models have been developed. One of the first models derived from that idea was the Statistical-Associating-Fluid Theory (SAFT) (Chapman et al. [12, 13] Huang and Radosz [14, 15]). 

Here, A is the ideal-gas contribution represents the hard-chain repulsion of the reference system. A P and A account for the Helmholtz energy contributions due to attraction (dispersion) and hydrogen bonding (association), respectively. To account for the fact that at least some of the species carry charges, this model was combined with a Debye-Hiickel theory to describe the Helmholtz energy contribution A to a system that is caused by charging the species. 

Various equations of state have been developed to treat association ia supercritical fluids. Two of the most often used are the statistical association fluid theory (SAET) (60,61) and the lattice fluid hydrogen bonding model (LEHB) (62). These models iaclude parameters that describe the enthalpy and entropy of association. The most detailed description of association ia supercritical water has been obtained usiag molecular dynamics and Monte Carlo computer simulations (63), but this requires much larger amounts of computer time (64—66). 

It should be mentioned that in the last few years super-cooled water has attracted the interest of many scientists because of its exceeding properties and life at temperatures below 0 °C 1819). Speedy recently published a model which allows for the interpretation of the thermodynamic anomalies of supercooled water 20). According to this model there are hydrogen bonded pentagonal rings of water molecules which have the quality of self-replication and association with cavities. 

An interesting structural feature of the model compound (Fig. 1) is that two pairs of substituents (A — D and R — R ) are each brought close together through specific association via two NH O intermolecular hydrogen bonds between the inner O O... 

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