Strong hydrogen bonds

Bfi and 022- However, in the second binary, intermolecular forces between unlike molecules are much stronger than those between like molecules chloroform and ethyl acetate can strongly hydrogen bond with each other but only very weakly with them-... 

Moderate errors in the total pressure calculations occur for the systems chloroform-ethanol-n-heptane and chloroform-acetone-methanol. Here strong hydrogen bonding between chloroform and alcohol creates unusual deviations from ideality for both alcohol-chloroform systems, the activity coefficients show... 

In conclusion, the special influence of water on the endo-exo selectivity seems to be a result of the fact that this solvent combines in it three characteristics that all favour formation of the endo adduct (1) water is a strong hydrogen bond donor, (2) water is polar and (3) water induces hydrophobic interactions. 

Association Complexes. The unshared electron pairs of the ether oxygens, which give the polymer strong hydrogen bonding affinity, can also take part in association reactions with a variety of monomeric and polymeric electron acceptors (40,41). These include poly(acryhc acid), poly(methacryhc acid), copolymers of maleic and acryflc acids, tannic acid, naphthoHc and phenoHc compounds, as well as urea and thiourea (42—47). 

Strong hydrogen bonding among components retards adsorption. 

Poly(vinyhdene chloride) also dissolves readily in certain solvent mixtures (82). One component must be a sulfoxide or A/,Al-diaIk5lamide. Effective cosolvents are less polar and have cycHc stmctures. They include aUphatic and aromatic hydrocarbons, ethers, sulfides, and ketones. Acidic or hydrogen-bonding solvents have an opposite effect, rendering the polar aprotic component less effective. Both hydrocarbons and strong hydrogen-bonding solvents are nonsolvents for PVDC. 

The hydroxyl groups in poly(vinyl alcohol) contribute to strong hydrogen bonding both intra- and intermolecularly, which reduces solubiUty in water. The presence of the residual acetate groups in partially hydrolyzed poly(vinyl alcohol) weakens these hydrogen bonds and allow solubiUty at lower temperatures. 

Color from Vibrations and Rotations. Vibrational excitation states occur in H2O molecules in water. The three fundamental frequencies occur in the infrared at more than 2500 nm, but combinations and overtones of these extend with very weak intensities just into the red end of the visible and cause the blue color of water and of ice when viewed in bulk (any green component present derives from algae, etc). This phenomenon is normally seen only in H2O, where the lightest atom H and very strong hydrogen bonding combine to move the fundamental vibrations closer to the visible than in any other material. 

Nonthermoprocessible Condensation Polyimides. These are obtained from condensation of aromatic dianhydrides with aromatic diamines. They are linear noncross-linked resins but their rigid chain stmcture and strongly hydrogen-bonded character leads to systems which do not melt or soften before decomposition. 

In the solid state the CH tautomer (78a) is always readily identified, but the OH and NH tautomers (that, in some cases, coexist in the crystal (73CSC469)) are difficult to differentiate due to the strong hydrogen bonds that shift the u(CO) band to the region of pyrazole vibrations. This source of complications is not present in the fixed forms that can always be identified by their IR spectra, both in solution and in the solid state. 

In addition, the frequency cooo, as well as the tunneUng distance can also be extracted from the same empirical data. Thus all the information needed to construct a PES is available. Of course, this PES is a rather crude approximation, since all the skeleton vibrations are replaced by a single mode with effective frequency cooo and coupling parameter C. From the experimental data it is known that the strong hydrogen bond (roo < 2.6 A) is usually typical of intramolecular hydrogen transfer. 

The cellulose molecule is rigid and forms strong hydrogen bonds with adjacent molecules. It is thus insoluble and decomposes before softening on heating. Partial replacement of hydroxyl groups by acetyl groups has a number of effects ... 

The amount of polar monomer one would copolymerize with the alkyl acrylate monomer(s) very much depends on the type of polar monomer and the desired change in rheological properties one would like to achieve. Strong hydrogen bonding monomers, such as acrylic acid, methacrylic acid, acrylamide, or methacrylamide are typically used at levels of 12% or less of the total monomers. 

The simulated free surface of liquid water is relatively stable for several nanoseconds [68-72] because of the strong hydrogen bonds formed by liquid water. The density decrease near the interface is smooth it is possible to describe it by a hyperbolic tangent function [70]. The width of the interface, measured by the distance between the positions where the density equals 90% and 10% of the bulk density, is about 5 A at room temperature [70,71]. The left side of Fig. 3 shows a typical density profile of the free interface for the TIP4P water model [73]. 

The extraordinanly high polaiity of the fluonnated alcohols reflects their strong hydrogen-bonding capability [54] The P values of 10 2 for CF3CH2OH and 11 08 for (CF3)2CHOH compare with 10 6 and 12 1 for 50% formic acid and water, respectively [39]... 

Gerlt, J. A., Kreevoy, M. M., Cleland, W. W., and Frey, P. A., 1997. Understanding enzymic catalysis The importance of short, strong hydrogen bonds. Chemistry and Biology 4 259-267. 

Figure 27.6 Some typical planar complexes of nickel (11) (a) Ni(Mcft-acac)2). (b) Ni(Me-sal)2] and (c) [Ni(dmgll)2. (Note the short 0-0 distance which is due to strong hydrogen bonding.)...

Experimental reactivity patterns are based on solution behavior which are influenced by interactions between solvent and reacting molecules (especially ions). Compare electrostatic potential maps of 2-methyl-2-propyl cation and dimethylhydroxy cation. Identify sites that might form strong hydrogen bonds with water. Which ion will be better stabilized by its interaction with water ... 

The foregoing assumption that alkylation does not affect pKa values, which can be tested, is generally true to within ca. 0.3 pK units. Sometimes alkylation breaks a strong hydrogen bond (cf. 47, 48), and then the basicity of the alkylated and nonalkylated forms can differ considerably (for compound 47, by 0.5 to 0.9 pif units). Another implied assumption in this method is that the structures of the cations formed by the potentially tautomeiic compound and both alkylated forms are similar, which is not always true (cf. 49, 50). In these cases the method is not reliable. 

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