Hydroxyl protons resonance

FIGURE 32. H NMR spectrum of filipin III, 3 mM in DMSO-dg, recorded at 400 MHz and 25 °C. The expanded region contains nine hydroxylic proton resonances that fully exchange with deuterium oxide and correspond to the nine hydroxyl groups of filipin III. No apodization functions were applied prior to the Fourier transformation. Reproduced by permission of John Wiley Sons from Reference 50... 

When the mixture is cooled, the hydroxylic proton resonances shift to a lower field, and the extent of their shifts at -60°C is larger than those of individual solutions. This result suggests that lowering the temperature increased the dominance of 152 and 153 in the ground state and that photocycloadditions via such a hydrogen-bonded complex produce the endo adducts selectively. 

Figure 2. Predicted spectrum for the hydroxylic proton resonance of [(CH8)3PtOH h observed spectrum redrawn from Ref. 41...

Table 4 High-frequency H oxime (H7, H17, H27, HJ, aromatic (H3) and hydroxylic proton resonances correlated to Sn resonafl as obtained from the 2D H- Sn HM( spectrum of compound 1 in QD. Qiemical shift data are ven in ppm. V( Sn, H) coupling constants are given in Hz and were obtained from F2 slices of the 2D HMQC spectra presented in Figure 18. (Data from ref. [17])... 

The last point to be discussed for species mi is the bonding mode of this ligand C to the atoms Sn2 and Sn3. Two modes can be envisaged. They are shown in Figure 20. The 2D correlation features of the hydroxylic proton resonance at 10.90 ppm, associated with ligand C, enable a choice between... 

In this structure, two likely features, supported by experimental data, should be outlined. Firstly, the ligand C should be perpendicular to the plane Sn3-O40-Sn2. The identical intensities of the 2D HMQC crosspeaks H27-Sn2 and H27-Sn3 arising from V( Sn, H) coupling pathways are in agreement with this view. Secondly, as the hydroxylic proton resonance of ligand C at 10.90 ppm is rather sharp, in the same way as those around 14 ppm in both M and mi are, the proposed structure is likely to be stabilized by an intramolecular hydrogen bridge 029-H. . . 040. 

By cooling, and careful control of the pH of, aqueous solutions, it is possible to obtain well-resolved hydroxyl-proton resonances, and these also... 

The phenolic compounds characteristically display high field chemical shifts for the aromatic hydrogens ortho and para to the hydroxyl substituent. The single hydroxyl proton resonates at much lower field than the corresponding OH group of the alcohols but at higher field than that of the carboxylic acids. 

Observation of the hydroxyl proton resonance is also of value in differentiating between cyclic and acyclic forms of compounds. Thus D-erythrose-2,5-dichlorophenylhydrazone shows two doublets (OH-2 and OH-3) and a triplet (OH-4) and D-fucose-toluene-p-phenyl-hydrazone shows four doublets (OH-2 to OH-5). 

NMR data of substituted 3-hydroxythiophenes indicate that in cases where the hydroxy group is nonchelated (e.g., with alkyl substituents), the hydroxylic proton resonates between 5.6 and 6.7 ppm... 

Many of the properties of phenols reflect the polarization implied by the resonance description The hydroxyl oxygen is less basic and the hydroxyl proton more acidic in phenols than m alcohols Electrophiles attack the aromatic ring of phenols much faster than they attack benzene indicating that the ring especially at the positions ortho and para to the hydroxyl group is relatively electron rich... 

Clearly, in the case of (66) two amide tautomers (72) and (73) are possible, but if both hydroxyl protons tautomerize to the nitrogen atoms one amide bond then becomes formally cross-conjugated and its normal resonance stabilization is not developed (c/. 74). Indeed, part of the driving force for the reactions may come from this feature, since once the cycloaddition (of 72 or 73) has occurred the double bond shift results in an intermediate imidic acid which should rapidly tautomerize. In addition, literature precedent suggests that betaines such as (74) may also be present and clearly this opens avenues for alternative mechanistic pathways. 

Up to the present the principal interest in heteroaromatic tautomeric systems has been the determination of the position of equilibrium, although methods for studying fast proton-transfer reactions (e.g., fluorescence spectroscopy and proton resonance ) are now becoming available, and more interest is being shown in reactions of this type (see, e.g., references 21 and 22 and the references therein). Thus, the reactions of the imidazolium cation and imidazole with hydroxyl and hydrogen ions, respectively, have recently been demonstrated to be diffusion controlled. ... 

The 1H NMR spectra of the epimeric cyclohexanols in DMSO reveal that the hydroxyl proton in the axial alcohol shows a resonance absorption at a higher field than in the equatorial one, indicating that the conformational effect of the hydrogen bond influences the XH NMR chemical shifts128. 

The submitters purchased glacial acetic acid from Showa Denko K. K., Tokyo, Japan, and acetic anhydride from Riedel de Haen AG, Seelze-Hannover, Germany. A solution prepared from 4 volumes of glacial acetic acid, 1 volume of acetic anhydride, and a catalytic amount of p-toluenesulfonic acid was heated under reflux for 24 hours and distilled. The distillate, which contained 5% water and 4% acetic anhydride according to analysis of the proton magnetic resonance spectrum, was then used by the submitters. The water content was determined from the chemical shift of the hydroxyl proton. ... 

Rader, C. P. Hydroxyl Proton Magnetic Resonance Study of Aliphatic Alcohols. 

The H NMR spectram (CDClj, 500 MHz) of 12 showed two singlets (8 0.83 and 8 0.95), each integrating for three protons due to the C-18 and C-19 methyl protons. Three 3H doublets at 8 0.78 (J= 6.5 Hz), 8 0.79 (J= 6.5 Hz) and 8 0.85 (J = 7.0 Hz) were due to the secondary C-26, C-27 and C-21 methyl protons, respechvely. The C-3 methine proton resonated as a one-proton double doublet at 8 3.63 (JJ= 10.5 Hz and J2= 3.5 Hz) and its downfield chemical shift value was indicative of the presence of a geminal hydroxyl funchonality. A one-proton mulhplet at 8 5.21 was ascribed to the C-6 olefinic proton. The C-28 exocyclic methylene protons appeared as two broad singlets at 8 5.40 and 5.58. The C-NMR spectram (CDCl, 125 MHz) showed the resonance of all 28 carbon atoms. The combination of H and C-NMR data suggested that compound 12 has a sterol like structure as most of the H and C-NMR chemical shift values of 12 were similar to those of sterols reported in the literature [19, 20]. The H and C-NMR chemical shift values were assigned with the aid of COSY-45 , HSQC and HMBC spectral data. Compound 12 was found to have modest inhibitory activity against C. xerosis and S. aureus with minimal inhibitory concentration values of 82.35 and 146 pg/ml, respectively. 

Lunsford et al. (202) used trimethylphosphine as a probe molecule in their 31P MAS NMR study of the acidity of zeolite H-Y. When a sample is activated at 400°C, the spectrum is dominated by the resonance due to (CH3)3PH+ complexes formed by chemisorption of the probe molecule on Bronsted acid sites. At least two types of such complexes were detected an immobilized complex coordinated to hydroxyl protons and a highly mobile one, which is desorbed at 300°C. (see Fig. 45)... 

You may have wondered why the hydroxyl proton of ethanol produces a single resonance in the spectrum of Figure 9-23. It is quite reasonable to expect that the hydroxyl proton would be split by the neighboring methylene protons... 

Formation of intramolecular hydrogen bonds shows up clearly in the proton nmr spectra, as we have seen previously for the enol form of 2,4-pentanedione (Section 17-ID, Figure 17-1). Figure 26-1 shows the proton resonances of the nitrobenzenol isomers, and you will see that the ortho isomer has the OH proton resonance at much lower field than either the meta or para isomer. Only for the ortho isomer are the nitro and hydroxyl groups sufficiently close together to form an intramolecular hydrogen bond ... 

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