Hydrogen-bonding additives

Collagen triple helices are stabilized by hydrogen bonds between residues in dijferent polypeptide chains. The hydroxyl groups of hydroxyprolyl residues also participate in interchain hydrogen bonding. Additional stability is provided by covalent cross-links formed between modified lysyl residues both within and between polypeptide chains. 

The mineral oil has a rather simple spectrum (only carbon-hydrogen bonds). Additionally, as with solvents, a computer maybe used to subtract the mineral oil bands from the spectrum of the solid. 

Besides metal containing Lewis acids, non-metal additives have also found application in catalysis. These studies are quite pertinent to the development of artificial enzymelike catalysts. As there is a large number of Lewis basic sites in living systems able to be involved in hydrogen bonds, the analysis of the catalytic activity of hydrogen bonding additives would give some indication as to the existence of Diels-Alder reactions... 

The crown ether 11 has a trimethylammonium group reaching into the interior of the cavity and is complexed intramolecularly by short CH—O hydrogen bonds. Additional hydrogen bonds between the acidified CH3 groups and the iodide anion were confirmed by X-ray analysis. 

Finally, in the crystal structures of the chloroform and ethanol solvates of [(dppmSe)2Au]Cl [91] the ions are connected into chains by C-H - Cl hydrogen bonds, whereby the chloride accepts two hydrogen bonds. Additionally, there is a C-H - Cl contact from a solvent molecule in the chloroform solvate (Figure 5.56b) and an O- Cl contact involving the solvent in the ethanol solvate. 

Batchwise Fluorodediazoniation in Anhydrous Hydrogen Fluoride Containing Hydrogen-Bonding Additives... 

A third possibility of a mechanism leading to general acid catalysis is the equilibrium formation of a hydrogen-bonded addition compound of substrate and general acid, followed by slow decomposition of the addition complex to the products [27], Such a mechanism is not very likely for reactions in aqueous solutions. However, it has been suggested for the general acid catalyzed hydrolyses of ethyl orthoformate and ethyl orthoacetate in 60 % aqueous dioxane [28]. 

Q. Huo, K.C. Russell, R.M. Reblanc, Effect of Complementary Hydrogen Bonding Additives in Subphase on the Structure and Properties of the 2-Amino-4,6-... 

Only molecules with H attached to the electronegative atoms F, N, and O can hydrogen bond. Additionally, there must be lone pairs available for the H s to bond to. This is true only of (c) HjSOj. 

With all these reagents it can be assumed that the first step in the process involves the formation of an ester-halide (XVIII and XIX) or the hydrogen bonded addition complex (XX). Many compounds such... 

For the third route (in which optical configuration is retained) an internal displacement reaction (S i) has been postulated.20 26 Thus it is suggested that the ester halides (or the hydrogen bonded addition complex) undergo intramolecular rearrangement with elimination of the corresponding oxide in such a way that configuration is retained. 

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