H NMR Spectra of Alcohols

This proton splits signal for proton at C-2 into a doublet. 

The chemical shift of the hydroxyl proton is variable, with a range of 8 0.5-5 ppm, 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 strength in more concentrated solutions. 

FIGURE 13.19 The 200-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. 

An easy way to verify that a particular signal belongs to a hydroxyl proton is to add D2O. The hydroxyl proton is replaced by deuterium according to the equation  

Deuterium does not give a signal under the conditions of H NMR spectroscopy. Thus, replacement of a hydroxyl proton by deuterium leads to the disappearance of the OH peak of the alcohol. Protons bonded to nitrogen and sulfur also undergo exchange with D2O. Those bound to carbon normally do not, which makes this a useful technique for assigning the proton resonances of OH, NH, and SH groups. 

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Fig. 3. Temperature-dependent H NMR spectra of alcohol 8 in FSO3H/SO2CIF...

Section 24 15 The IR and H NMR spectra of phenols are similar to those for alcohols except that the OH proton is somewhat less shielded m a phenol than m... 

FIGURE 22.8 The 200-MHz H NMR spectra of (a) 4-methylbenzylamine and ( )) 4-methylbenzyl alcohol. The singlet corresponding to CH2N in (a) is more shielded than that of CH2O in (b). 

The H 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 NMR chemical shifts . 

The 2H-NMR spectra of these derivatized carboxylic acids sometimes are a powerful and simple alternative for the estimation of optical purity. Similar analysis of diastcrcomcric derivatives of a-deuteriated primary alcohols with (5)-2-0-acetylmandelic acid and primary amines with (-)-(1 S, 2/ )-camphanoy 1 chloride is also possible. However, in most cases the shift differences in the simple H-NMR spectra of the same derivatives are large enough to obtain the diastereomeric ratio. Shift differences of the two a-methylenic diastereotopic hydrogens are typically between <5 = 0.05 and 0.2. 

The 1,3,2-oxazaphospholanes 90a-c and 91a-c were obtained in excellent yields by cyclization of the amino alcohols 89a -c with ethyl phosphonic dichloride in toluene in the presence of triethylamine. The mixture of diastereomers at the phosphorus center were separated by silica gel chromatography. Assignation of the absolute configurations was possible through a complete analysis of the H NMR spectra of the diastereomers and was confirmed by X-ray analysis for one derivate (Scheme 41). 

Solutions of MnX2 in the alcohols give [Mn(ROH)s]2+ species,212 and these cations have been isolated as crystalline solids for R = Me, Et. In more concentrated solutions, the species [MnX (ROH)6 B](2w,)+ have been detected by EPR and H NMR spectra. The alcohol ligands are easily replaced by water. 

Alcohok. When using the H NMR spectra of MTPA esters to determine the enantiomeric purity of alcohols, the MTPA methoxy peaks tend to be most useful. This technique can be sensitive enough to detect as little as 1% of the minor alcohol enantiomer. The enantiomeric purity of chiral alcohols (1) and (2) has been determined this way. The enantiomeric purity of primary alcohols (3) and (4), in which the asymmetric center is not the carbinol carbon, has also been determined by H NMR analysis of their MTPA esters. A slight variation of this methodology is the use of shift reagents like Eu(fod)3 to increase the chemical shift separation between diastereotopic MeO peaks this procedure has been used in the analysis of alcohols (S) and (6). ... 

Bhar and his associates studied carboxylic acids in water (213, 214). As water is added to either pure acetic acid or propionic acid, b decreases steadily except for a curious hump in the curve at 50 percent water by volume. This feature is not evident in the acetic acid-water resonance data given by Gutowsky and Saika (851). Batdorf conducted NMR studies of phenols (148). His results are similar to but less detailed than those shown in Fig. 4-4. Crawford and Foster used the spin echo technique for NMR spectra of alcohols but not specifically with interest in H bonding (460). 

Other carboxylic acids such as 55 have been used to make corresponding diastereoisomeric esters. The choice of aromatic substituent in 55 is made on the basis of the greater anisotropy of the three fused aromatic rings in 55 with respect to phenyl. It has recently been possible to assign configuration to a pair of enantiomeric alcohols directly from the H NMR spectra of their esters with 55. The discussion goes beyond the scope of this text, but for details the work of Fukushi et al. 1 Takahashi et a/.18 and Seco et al 9 should be consulted. 

Petroff and co-workers reported a quantitative analysis of the H NMR spectra of six CSF samples from three patients. TTiese included a 34-year-otd man presenting with seizures several hours after injecting heroin and cocaine while intoxicated with alcohol, and a 7-month-old girl who presented as a febrile, cyanotic hypotensive in a coma. The H NMR spectrum of the CSF of the drug overdose victim showed clear and abnormally elevated signals for citrate, myo-inositol, creatinine/creatine and lactate. 

H NMR spectra of four isomeric alcohols with formula C9H12O are shown in Figure 13.48. Assign a structure for each alcohol and assign the peaks in each spectmm. 

Section 22.15 The IR and H NMR spectra of phenols are similar to those for alcohols, except that the OH proton is somewhat less shielded in a phenol than in an alcohol. In NMR, an OH group deshields the carbon of an aromatic ring to which it is attached. An OH group causes a shift in the UV-VIS spectrum of benzene to longer wavelengths. The effect is quite large in basic solution because of conversion of OH to 0. ... 

In order to confirm this deduction and the proposed regioselectivity of the Diels-Alder type reaction between a chalcone and a dehydropren-ylphenol, two model compounds 115 and 116 were prepared in 46% resp. 25% yield by a Diels-Alder reaction between /ra 5-chalcone and 3-methyl-l-phenyl-l,3-butadiene (250 °C, 5h). Their structures were established by X-ray crystallography and are shown in Fig. 24. The H-NMR spectra of 115 and 116 were compared with those of alcohols 117 and 118 obtained by reduction. Signals of the protons on the relevant carbon atoms of alcohols 117 and 118 were shifted by 1.16 ppm and 1.61 ppm to higher field than the corresponding signals in 115 and 116, as shown in Fig. 25. 

The most distinctive feature of the H-NMR spectra of ethers is the chemical shift of hydrogens on the carbons bonded to the ether oxygen. Signals for this type of hydrogen fall in the range 8 3.3 to 4.0, which corresponds to a downfield shift of approximately 2.4 units compared with their normal position in alkanes. The chemical shifts of H—C—O— hydrogens in ethers are similar to those seen for comparable H—C—OH hydrogens of alcohols. 

FIGURE 15.45 Two H NMR spectra of ethyl alcohol show different shifts for the OH signal. 

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