Hydroxyl proton spectra

The chemical shift of the hydroxyl proton is variable with a range of 8 0 5-5 depending on the solvent the temperature at which the spectrum is recorded and the concentration of the solution The alcohol proton shifts to lower field m more concen trated solutions... 

MHz H NMR spectrum of benzyl alcohol The hydroxyl proton and the methylene protons are vicinal but do not split each other because of the rapid intermolecular exchange of hydroxyl protons... 

NMR The H NMR signals for the hydroxyl protons of phenols are often broad and their chemical shift like their acidity lies between alcohols and carboxylic acids The range is 8 4-12 with the exact chemical shift depending on the concentration the solvent and the temperature The phenolic proton m the H NMR spectrum shown for p cresol for example appears at 8 5 1 (Figure 24 4)... 

Reduction of epoxide 21 with lithium aluminium hydride gave a crystalline branched-chain methyl heptoside derivative 24. The NMR spectra of compounds 21 and 24 were very similar. In the spectrum of compound 24 the disappearance of the two sharp doublets at r 6.80 and 7.45 (2 protons) and the appearance of a singlet at r 8.65 (3 protons) is consistent with the reductive cleavage of epoxide 21 to give a substance 24 with a methyl substituent. The multiplet at r 7.40-8.50 ( 5 protons ) was assigned to the four protons of the two methylene groups and the hydroxylic proton. 

When the H NMR spectrum of an alcohol is run in dimethyl sulfoxide fDMSO) solvent rather than in chloroform, exchange of the O—H proton is slow and spin-spin splitting is seen between the O-H proton and C-H protons on the adjacent carbon. What spin multiplicities would you expect for the hydroxyl protons in the following alcohols ... 

The intensities (heights) of the peaks are proportional to the numbers of protons that they represent. The three peaks in the ethanol spectrum, for example, have overall intensities in the ratio 3 2 1, which is what we would expect for the three methyl, two methylene, and one hydroxyl protons. 

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. ... 

If you take a pure sample of ethanol, and run its NMR spectrum in dry CDCI3, the hydroxyl proton will appear as a well-defined triplet, which couples to the adjacent -CH2-, rendering it a multiplet. This is because the hydroxyl proton remains on the oxygen for relatively long periods of time, as there is nothing in the solution to entice it off, i.e., exchange (if any) is said to be very slow on the NMR timescale (less than about 1 s). 

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... 

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... 

The H-NMR spectra (Table I) show no evidence of tautomerism of 1-hydroxypyrroles to 2H- or 3//-pyrrole 1-oxides and are similar to those of corresponding pyrroles. The hydroxyl proton is not always seen, as in the case of 1-hydroxyindole, and is easily exchanged out by deuterium oxide. The H-NMR spectrum of 2-cyano-2-methyl-2//-pyrrole 1-oxide (2) in dimethyl sulfoxide (DMSO) was unambiguous (Table I), but in deuter-iochloroform, the 3- and 4-protons appeared at the same position. 

When a proton is coupled to two non-equivalent sets of neighbouring protons more complex multiplets result this is illustrated by the spectrum of pure ethanol (Fig. 3.67). Thus the methylene protons are coupled to the three methyl protons, giving rise to a quartet, and are further coupled to the hydroxyl proton which therefore causes each of the peaks of the quartet to appear as a doublet. The multiplet therefore consists of eight peaks due to the two overlapping quartets i.e. (N -I- 1)(M + 1). On occasions there may be difficulty in recognising the components of these more complex multiplets, as some peaks may be superimposed. 

The spectrum of a solution in deuterochloroform (Fig. 3.65) shows three absorptions at <5 4.5, 5.08 and 7.3 with an intensity ratio of 2 1 5. The effect of adding a few drops of deuterium oxide to the sample tube and shaking vigorously is shown in the re-recorded spectrum (Fig. 3.66). The absorption at S 5.08 in the original spectrum which disappears on deuteration is clearly due to the hydroxyl proton. 

Dissolve 20 g (0.13 mol) of the cyano ester in 100 ml of rectified spirit and add a solution of 19.2g (0.295 mol) of pure potassium cyanide (CAUTION) in 40 ml of water. Allow to stand for 48 hours, then distil off the alcohol on a water bath. Add a large excess of concentrated hydrochloric acid and heat under reflux for 3 hours. (CAUTION hydrogen cyanide evolved.) Dilute with water, saturate the solution with ammonium sulphate and extract with four 75 ml portions of ether. Dry the combined ethereal extracts with anhydrous sodium sulphate, and distil off the ether. Recrystallise the residual acid from excess concentrated hydrochloric acid, and dry in the air. The yield of pure 2,2-dimethylsuccinic acid, m.p. 141-142 °C, is 12 g (63%). The p.m.r. spectrum is recorded in trifluoracetic acid and reveals signals at S 1.48 (s, 6H, Me2) and 2.92 (s, 2H, CH2) the hydroxyl proton is not observed. 

The NMR spectrum is rather simple as all peaks are singlets. The 12-proton singlet at 8 1.2 ppm must correspond to four equivalent methyl groups and the four-proton singlet at 8 1.6 ppm to two equivalent methylene groups. No nonequivalent protons can be vicinal, because no splitting is observed. The two-proton singlet at 8 2.0 ppm is due to the hydroxyl protons of the diol. 

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