Hydrogen-bonding association

Another difficulty is that the extent to which hydrogen bonded association and ion-pairing influence the observed kinetics has yet to be determined. However the high order of the reaction in the stoichiometric concentration of nitric acid would seem to preclude a transition state composed only of a nitronium ion and an aromatic molecule. 

Bond dissociation energies (BDEs) for the oxygen—oxygen and oxygen— hydrogen bonds are 167—184 kj/mol (40.0—44.0 kcal/mol) and 375 kj/mol (89.6 kcal/mol), respectively (10,45). Heats of formation, entropies, andheat capacities of hydroperoxides have been summarized (9). Hydroperoxides exist as hydrogen-bonded dimers in nonpolar solvents and readily form hydrogen-bonded associations with ethers, alcohols, amines, ketones, sulfoxides, and carboxyhc acids (46). Other physical properties of hydroperoxides have been reported (46). 

It is seen that the three values for the equilibrium constant (k) range from 0.00443 to 0.00565 with an average value of 0.00504. The two values for the densities of the methanol/water associate are in reasonable agreement and have a magnitude that would be expected for the hydrogen bonded associate. 

In solution and in the solid state, imidazole and its N2-unsubstituted derivatives form large hydrogen-bonded associates 13 (Scheme 8) [76AHC(S1), p. 266 84CHEC-I(5)345,84JPC5882 96CHEC-II(3)77 97JST(415)187]. 

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. 

Ethyl cellulose and cellulose triacetate have been shown to form hydrogen bonded associates with dichloromethane (10,30). If this is so, then cellulose triacetate-dichloromethane interaction will be favored over polystyrene-cellulose triacetate interaction and thus no adsorption should be expected. 

Apart from the increased catalytic efficiency, this structure design produced two positive side effects. In contrast to monofunctional (thio)ureas, which exhibit low solubility in nonpolar solvents due to intermolecular hydrogen-bonding association, tertiary amine thioureas of type 12 revealed intramolecular hydrogen bonding between the amine group and the amide protons making these (thio)ureas soluble in nonpolar reaction media such as toluene. The analysis of the X-ray crystal-... 

Recently, a new class of supramolecular CpRu-containing catalysts for hydration of alkynes has emerged. These catalysts are based on the supramolecular self-assembly of monodentate ligands through hydrogen bonding association, as shown in Scheme 10.9 [41-43]. The remarkable activity of catalytic systems such as 15-17... 

The value is a key measurement of the strength of the hydrogen bonding associ-... 

Lehn and Rotello s groups extensively studied diacyldiaminopyridines that form triple hydrogen bonded associated structures with uracil and thymine groups (Gulik-Krzywicki et al. 1993 Carroll et al. 2003 Stubbs and Week 2003 Sanyal et al. 2004). lUian et al. (2000) studied the formation of vesicles from mixtures of randomly functionalized complementary copolymers containing thymine groups and... 

Other examples of interpolymer complexation due to hydrogen bonding include complexes of poly(ethylene-co-methacrylic acid) with polyethers, poly(2-vinylpyridine), and polyethyloxazoline [107-109], and PAA with poly(vinyl alcohol-co-vinyl acetate) [110]. PAA has even been shown to form stable interchain hydrogen bonded association under high shear flow [111]. 

The hydrogen-bonding association of amino acid esters with 1-phenyl-2,2,2-trifluoroethanol is sufficient to permit NMR to be used as a method for determining the optical purities of a-amino acids [43]. 

Much of their backbone chain is Involved in helical hydrogen-bonded associations. Folding is maintained by both internal hydrogen and hydrophobic bonds as well as by disulfide bonds. 

Arylation, olefins, 187, 190 Arylketimines, iridium hydrogenation, 83 Arylpropanoic acid, Grignard coupling, 190 Aspartame, 8, 27 Asymmetric catalysis characteristics, 11 chiral metal complexes, 122 covalently bound intermediates, 323 electrochemistry, 342 hydrogen-bonded associates, 328 industrial applications, 8, 357 optically active compounds, 2 phase-transfer reactions, 333 photochemistry, 341 polymerization, 174, 332 purely organic compounds, 323 see also specific complexes Asymmetric induction, 71, 155 Attractive interaction, 196, 216 Autoinduction, 330 Axial chirality, 18 Aza-Diels-Alder reaction, 220 Azetidinone, 44, 80 Aziridination, olefins, 207... 

Purely organic catalysts (Continued) electrochemistry, 342 hydrogen-bonded associates, 328 phase-transfer reactions, 333 photochemistry, 341 polymerization, 332... 

Reactions via Covalently Bound Intermediates / 323 Reactions via Hydrogen-Bonded Associates / 328... 

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