Formate complexes, hydrogen-bonded

Excess Volume Comparison Figure 7.5 compares V for the three systems for which we have compared H, G, and 5, plus the (cyclohexane + decane) system.5 The comparatively large negative for the (ethanol + water) system curve (4) can be attributed to the decrease in volume resulting from the formation of hydrogen-bonded complexes in those mixtures. The negative for the (hexane + decane) system curve (3) reflects an increased packing... 

Sulphoxides and sulphones form hydrogen bonds with proton donors and association complexes with metallic salts by using either the oxygen atom or the sulphur atom in their S—O linkages. The capability for the formation of hydrogen bonds or complexes depends... 

C. Colominas, F. J. Luque, and M. Orozco, Tautomerism and protonation of guanine and cytosine. Implications in the formation of hydrogen-bonded complexes, J. Am. Chem. Soc. 118 6811 (1996). 

K. Le Barbu Debus, N. Seurre, F. Lahmani, and A. Zehnacker Rentien, Formation of hydrogen bonded bridges in jet cooled complexes of a chiral chromophore as studied by IR/UV double resonance spectroscopy. 2 Naphthyl 1 ethanol/(methanol)n j 2 complexes. Phys. Chem. Chem. Phys. 4, 4866 4876 (2002). 

The scale of hydrogen-bond basicity p hb, initially developed by Taft and coworkers14, has been extended by Abraham and coworkers81, and is based on the formation of hydrogen-bond complexes of a base B with a hydrogen-bond reference donor as 4-fluorophenol in CCI4 at 25 °C ... 

Fig. 7.4. Conformations of (a) free valinomycin and (b) of its potassium complex. The carbonyl oxygen atoms, P, P, M and M are in especially exposed positions, so that they can initiate complexation of potassium ion. During complexation, hydrogen bonds 1 and 2 are broken, so that oxygen atoms R and R can take part in the co-ordination of the cation. Further smaller conformation changes allow oxygen atoms Q and Q to partake in formation of new hydrogen bonds, the molecule thus attaining the final round shape (see [44a ]). (By permission of the American Association for Advancement of Science.)...

Generally, the formation of hydrogen-bonded complexes is regarded as a very fast, diffusion-controlled process with no energy barrier. On the other hand, even ultrafast molecular reorientations in solution require energy for reorganization of... 

Another example is the separation of several sulfonamides in acetonitrile by adding silver ions. Compounds such as N-containing heterocyclics were found to build selective charge transfer complexes with Ag+, which improves the selectivity of the separation. Phenols, carboxylic acids, and alcohols interact with anions such as CIO, BE, NO, Cl t,SO , and Cl in acetonitrile as solvent. The resulting electrophoretic mobility of the weak Bronsted acids (HA) in the presence of such anions is the result of the formation of complexes of the type [X. .. HA] due to the formation of hydrogen bonds (13). 

For moderate pH values, perhaps between 2 and 12, the reaction coordinate leading to oxidation of dimethyl sulfide by H2O2 involves 0-0 bond cleavage with the formation of the S—O bond. Under these conditions, water molecules can stabilize the transition complex via specific interactions including formation of hydrogen bonds with H2O2. 

ThermodynaMc Smdy of Complex Formation by Hydrogen Bonding in Halo-genoalkane-Oxygenated Solvent Mixtures—Halothane With Propyl Ether, Isopropyl Ether, 1,4-Dioxane, and 2,5-Dioxahexane (Dohnal et al., 1996)... 

Worth mentioning are some relevant studies on the prototropic exchanges of azoles in excited states involving the formation of hydrogen-bonded complexes [(7a) - (7b)] via Si (85JPC399) in complexes with acetic or via Ti in complexes with benzoic acid (83JA6790), or intramolecular complexes, as in the case of 2-(2 -hydroxy-5 -methylphenyl)benzotriazole (82JCP4978). 

When two polymeric systems are mixed together in a solvent and are spin-coated onto a substrate, phase separation sometimes occurs, as described for the application of poly (2-methyl-1-pentene sulfone) as a dissolution inhibitor for a Novolak resin (4). There are two ways to improve the compatibility of polymer mixtures in addition to using a proper solvent modification of one or both components. The miscibility of poly(olefin sulfones) with Novolak resins is reported to be marginal. To improve miscibility, Fahrenholtz and Kwei prepared several alkyl-substituted phenol-formaldehyde Novolak resins (including 2-n-propylphenol, 2-r-butylphenol, 2-sec-butylphenol, and 2-phenylphenol). They discussed the compatibility in terms of increased specific interactions such as formation of hydrogen bonds between unlike polymers and decreased specific interactions by a bulky substituent, and also in terms of "polarity matches" (18). In these studies, 2-ethoxyethyl acetate was used as a solvent (4,18). Formation of charge transfer complexes between the Novolak resins and the poly (olefin sulfones) is also reported (6). 

Complex formation between PEG and PMAA was reported in Refs. [55, 56]. Complex properties and structure were studied in detail in papers by Kabanov, Papisov and their coworkers. It was shown that the stability of the complexes is a result of action of two factors the formation of hydrogen bonds between carboxylic groups of PMAA and oxygen atoms of PEG and the hydrophobic interactions. 

It should be mentioned that the value of yInax for the complexes, that are saturated with PEG of relatively high molecular weight (6000), is larger than 1.0 (Ymax = 1.5). Thus there are 1.5 units of PEG per one unit of PMAA instead of 1 per 1 corresponding to the maximum number of the hydrogen bonds between two polymer components. This discrepancy can be explained by the fact that macromolecules of PEG form loops in the complex. The units of loop sections do not participate in the formation of hydrogen bonds. 

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