Hydrogen bond phenols and

A different approach is to use chemical shifts. These are very sensitive to differences in chemical surroundings. The chemical shifts of hydrogen bonded phenolates and quinones can be estimated. In addition, using a set of compounds with different equilibrium constants and extrapolating to a mole fraction of one, the chemical shift of the proton transferred form can be estimated. Using the above estimated chemical shifts it can be estimated that the o-quinonoid form 48B contributed ca 65% to the proton transferred form. ... 

Polyamide Partition chromatography due to polar interactions (e.g. hydrogen bonds) Phenolic and polyphenohc natural substances... 

The urea usually is added to the finished PF-resin and causes a distinct decrease of the viscosity due to disruption of hydrogen bonds [95] and due to dilution effects. There is obviously no co-condensation of this post-added urea with the phenolic resin. Urea only reacts with the free formaldehyde of the resin forming methylols, which, however, do not react further due to the high pH [19]. Only at the higher temperatures of the hot-press does some phenol-urea co-condensation occur [93,94,96]. 

Isotope labeling by derivative formation with deuterated reagents is useful for the preparation of analogs such as dg-acetonides, da-acetates, da-methyl ethers, dg-methyl esters, etc. The required reagents are either commercially available or can be easily prepared. (The preparation of da-methyl iodide is described in section IX-F. Various procedures are reported in the literature for the preparation of dg-acetone, da-diazometh-ane57.i63.i73 and da-acetyl chloride. ) These reactions can be carried out under the usual conditions and they need no further discussion. A convenient procedure has been reported for the da-methylation of sterically hindered or hydrogen bonded phenolic hydroxyl functions by using da-methyl iodide and sodium hydroxide in dimethyl sulfoxide solution. This procedure should be equally applicable to the preparation of estradiol da-methyl ether derivatives. 

M. Shi and Y.-L. Shi reported the synthesis and application of new bifunctional axially chiral (thio) urea-phosphine organocatalysts in the asymmetric aza-Morita-Baylis-Hillman (MBH) reaction [176, 177] of N-sulfonated imines with methyl vinyl ketone (MVK), phenyl vinyl ketone (PVK), ethyl vinyl ketone (EVK) or acrolein [316]. The design of the catalyst structure is based on axially chiral BINOL-derived phosphines [317, 318] that have already been successfully utilized as bifunctional catalysts in asymmetric aza-MBH reactions. The formal replacement of the hydrogen-bonding phenol group with a (thio)urea functionality led to catalysts 166-168 (Figure 6.51). 

Little comment can be made about the hydrogen-bonded OH groups that absorb close to 3300 cm."1. It is unlikely, however, within the rank range of resinites covered here that much variation in the intensity of this absorption would be recorded. The broad region of absorption between 1100 and 1300 cm."1 common to vitrinite and sporinite spectra is also found in the resinite spectra. The peak at 1270 cm. 1 almost certainly corresponds to the 1250 cm."1 band assigned by other workers to hydrogen-bonded phenolic structures. Fol-... 

Some compounds, such as highly substituted alcohols and ortho substituted phenols, are unable, for steric reasons, to form polymeric hydrogen bonded species, and hence they exist only as dimers which gives rise to sharp absorption in the 3550-3450cm-1 region. In these instances hydrogen bonds are also broken on dilution with the consequence that the absorption intensity and position change. 

The mechanism shown in Scheme 4.9 has been proposed for the hydrogen atom transfer from phenols (ArOH) to radicals (Y ) in non-aqueous solvents, a kinetic effect ofthe solvent (S) being expected when ArOH is a hydrogen bond donor and the solvent a hydrogen bond acceptor. Steps with mechanistic rate constants k, k-1 and k>, involve proton transfer (the latter two near to the diffusion-controlled limit), and kj involves electron transfer. The step with rate constant fco involves a direct hydrogen atom transfer, and the other path around the cycle involves a stepwise alternative. 

Intramolecular hydrogen bonds form at the expense of intermolecular ones, and intramolecularly hydrogen-bonded phenols have lower boiling points than isomers in which only intermolecular hydrogen-bonding is possible. 

Proton transfer (process III) in the excited state, which can be followed by the emission of the ionic form of a hydrogen-bonded phenolate anion [A- - BH+(B) —process V]. A large shift is then expected in the excitation spectrum and the dispersed fluorescence spectra typical of A. ... 

CHARGE FLUCTUATIONS OF THE HYDROGEN BOND NETWORK AND PROTON TRANSFER ASSISTED BY THE SOLVENT IN PHENOL-WATER CLUSTERS... 

The influence of substitution of either phenol, as proton donor, or aromatic proton acceptors has been indicated to be almost of the same magnitude on hydrogen bonding (Ryabokobylko and Chekunov, 1970). However, both electron-donor and electron-withdrawing substituents have been found to decrease the degree of selfassociation of phenol (Vanderborgh et al., 1970). 

The foregoing information suggested a 17-hydroxy-A-propionyl-indoline structure, and this was fully confirmed by the NMR-spectrum (Table IV) which showed the presence of three aromatic protons and a hydrogen-bonded phenolic hydroxyl group (singlet at 10.88 8). More important, the portion of the spectrum due to aliphatic protons was very similar to that of aspidolimine (LIII), except that no peaks were found that corresponded to a methoxyl group or a terminal methyl of an ethyl side chain. Other characteristic features of the aspidospermine (II)... 

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