OH Proton Chemical Shifts Research Articles

Experimental and theoretical comparison of the vibrational and NMR spectra of novel 6-6’-(1E-1’E)-(Propane-1,3Diylbis (Azanylyidene)) Bis (Phenylmethylylidene)) Bis (3-Octyloxy) Phenol), NBO and molecular docking studies

The characterization study of the synthesized novel compound 6-6’-(1E-1’E)-(Propane-1,3Diylbis(Azanylyidene))Bis(Phenylmethylylidene))Bis(3-Octyloxy)Phenol) (C45H58N2O4) was done by FT-IR, Raman and NMR spectra. Vibrational analysis was realized with normal coordinate treatment, and vibrational modes were assigned in the mid-IR region. The 13C and 1H -NMR spectra of the title compound were measured in DMSO and chloroform, and the corresponding chemical shifts were calculated in the different basis sets (6-31++G(d,p), 6-311G(2d,p), 6-311++G(2d,p), TZVPP) of DFT-B3LYP with continuum models. The vibrational and NMR spectroscopies show that the existence of the intramolecular resonance-assisted hydrogen bonds(O-H...N) results in the redshift of OH vibrational modes and its high proton chemical shifts (ca. 16 ppm), as confirmed by X-ray crystal structure and NRT studies.13C NMR chemical shifts of the Schiff base bond are determined as ca. 174 ppm. The calculations indicate that both the intramolecular hydrogen bond strength and the OH-proton chemical shift increase with increasing solvent polarity. The molecular docking studies reveal that the title ligand has the potency of inhibition against the VIM-2 and NDM-1 active sites of metallo-β-lactamase receptor.

1H-NMR as a structural and analytical tool of intra- and intermolecular hydrogen bonds of phenol-containing natural products and model compounds.

Experimental parameters that influence the resolution of 1H-NMR phenol OH signals are critically evaluated with emphasis on the effects of pH, temperature and nature of the solvents. Extremely sharp peaks (Δν1/2 ≤ 2 Hz) can be obtained under optimized experimental conditions which allow the application of 1H-13C HMBC-NMR experiments to reveal long range coupling constants of hydroxyl protons and, thus, to provide unequivocal assignment of the OH signals even in cases of complex polyphenol natural products. Intramolecular and intermolecular hydrogen bonds have a very significant effect on 1H OH chemical shifts which cover a region from 4.5 up to 19 ppm. Solvent effects on –OH proton chemical shifts, temperature coefficients (Δδ/ΔT), OH diffusion coefficients, and nJ(13C, O1H) coupling constants are evaluated as indicators of hydrogen bonding and solvation state of phenol –OH groups. Accurate 1H chemical shifts of the OH groups can be calculated using a combination of DFT and discrete solute-solvent hydrogen bond interaction at relatively inexpensive levels of theory, namely, DFT/B3LYP/6-311++G (2d,p). Excellent correlations between experimental 1H chemical shifts and those calculated at the ab initio level can provide a method of primary interest in order to obtain structural and conformational description of solute-solvent interactions at a molecular level. The use of the high resolution phenol hydroxyl group 1H-NMR spectral region provides a general method for the analysis of complex plant extracts without the need for the isolation of the individual components.

Why Is an Aged Whiskey Highly Valued?

After fermentation followed by distillation, whiskey is stored in oak barrels for several years to some tens of years, a process known as aging. During the aging process in oak barrels, colorless distillates turn to amber distillates and the sharp or raw odor typical of fresh whiskey distillates is modified to a rounded, soft, and mellow aroma. Various compounds such as fragrances and polyphenols in the oak are extracted by the whiskey, while water or unpleasant odors pass out of the barrels through the boards. Aging of whiskey increases the potentiation of the response of GABAA receptor, a main inhibitory neurotransmitter receptor and the target of mood-defining drugs such as tranquilizers, sleeping drugs and anesthetics. Aging of whiskey also increased 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity, i.e., antioxidative activity. The increase of acidic and phenolic components in whiskey, which is gained in oak wood barrels during aging, shifted OH-proton chemical shift values toward the lower field proportionally, suggesting that these compounds strengthened the hydrogen-bonding structure of water-ethanol in whiskey and may make the whiskey taste good. These changes of minor components in whiskey during aging might improve the flavor and taste and make aged whiskey highly valued.

Diols as hydrogen bond acids: 1H NMR study of the hetero‐association of pyridine with sterically hindered EDOT diols

AbstractThe hetero‐association of pyridine with the cis and trans methyl‐3,4‐ethylenedioxy‐2‐[3‐(2,2,4,4‐tetramethylpentan‐ 3‐ol)]thiophenes (Me‐EDOT alcohols), 3,4‐ethylenedioxy‐2,5‐bis[3‐(2,2,4,4‐tetramethylpentan‐3‐ol)]thiophene (EDOT diol) and methyl‐3,4‐ethylenedioxy‐2,5‐bis[3‐(2,2,4,4‐tetramethylpentan‐3‐ol)]thiophene (Me‐EDOT diol) has been studied by 1H nuclear magnetic resonance (NMR) spectroscopy in benzene at 298 K. Self‐consistent association constants for the syn (S), anti‐syn (AS) and syn‐syn (SS) rotamers are determined from the variation of the OH proton chemical shift and of the rotamer composition with the pyridine concentration. The bridge methyl group has no effect upon the association constant of a syn OH group. Association constants are the same for the syn OH groups in the AS and syn‐anti (SA) rotamers of the diols, being slightly higher than for the alcohols. In contrast, values for a single syn OH group in the SS rotamers of the diols are significantly lower. Hydrogen bond acidity A values, determined for some congested alcohols and diols by the NMR method of Abraham, confirm that the syn OH protons of SS rotamers are less acidic than the single syn OH proton of an AS or SA rotamer. A values, with the notable exceptions of those for propan‐1,3‐diol and butan‐1,4‐diol, correlate with pyridine hetero‐association constants. Copyright © 2008 John Wiley & Sons, Ltd.

Self‐ and hetero‐association of sterically hindered tertiary alcohols

AbstractSelf‐association constants for 2,2,4,4‐tetramethyl‐3‐alkylpentan‐3‐ols are so small as to be negligible in comparison with hetero‐association constants for the same alcohols with a moderately strong base. Equilibrium constants were determined by the NMR titration method for the hydrogen bonding association of this and two other series of sterically hindered alcohols with pyridine, in benzene as solvent. Steric effects are small even when the 3‐alkyl substituent is very bulky. The acidity of the OH hydrogen in 2,2,4,4‐tetramethyl‐3‐phenylpentan‐3‐ols increases slightly with the electron‐withdrawing ability of the para substituent (Hammett reaction constant, 0.3). The syn rotamer of a 2‐methyl derivative, where the methyl and OH groups are close, has a lower association constant than the anti rotamer. In the case of 2,2,4,4‐tetramethyl‐3‐(2‐thienyl)pentan‐3‐ols a second approach, based on the variation of the syn/anti ratio with the pyridine concentration, gives results concordant with those of the NMR method. The association constants predict accurately syn/anti ratios and syn OH proton chemical shifts in neat pyridine. The unusually large temperature coefficients of OH proton shifts in pyridine are due in part to the variation of the association constant. Copyright © 2005 John Wiley & Sons, Ltd.

Solute effects on the interaction between water and ethanol in aged whiskey.

The hydrogen-bonding structure of water-ethanol in whiskey was examined on the basis of (1)H NMR chemical shifts of the OH of water and ethanol. Phenolic acids and aldehydes (gallic, vanillic, and syringic acids; vanillin and syringaldehyde) exhibited their structure-making effects regardless of the presence or absence of 0.1 or 0.2 mol dm(-3) acetic acid. The OH-proton chemical shifts were measured for 32 malt whiskey samples of a distillery, aged for 0-23 years in five different types of casks. The OH-proton chemical shift values of the whiskies shifted toward the lower field in proportion to their contents of total phenols. It can be concluded that the strength of the hydrogen bonding in aged whiskies is directly predominated by acidic and phenolic components gained in oak wood casks and not dependent on just the aging time.

Effects of Salts, Acids, and Phenols on the Hydrogen-Bonding Structure of Water−Ethanol Mixtures

The effects of salts, acids, and phenols on the hydrogen-bonding structure of water in 20% (v/v) EtOH−H2O solution were investigated on the basis of 1H NMR chemical shifts of the OH of water and ethanol. It was found that many salts caused structure breaking of water while a few metal salts, such as MgCl2 and KF, had a strengthening effect. The OH proton chemical shifts caused by the presence of alkali-metal and alkaline-earth-metal ions or anions (halides, NO3-, ClO4-, SO42-) from strong acids were related to the sizes and charges of the ions. Not only acids (H+ and HA, undissociated acids) but also bases (OH- and A-, conjugate-base anions from weak acids) had the effect of strengthening the structure of water; the degree of the effect was dependent on the acid strength (pKa). The proton exchange between water and ethanol molecules in 60% (v/v) EtOH−H2O solution was examined, on the basis of the coalescence of two signal peaks of water and ethanol as well as the further low-field shift in 1H NMR spectra with increasing concentration of solutes. Although it has been already reported that the proton exchange between water and ethanol molecules is promoted by strong acids and bases, a distinct proton exchange was also observed in the neutral solution, i.e., by the addition of phosphate pH buffer solution (pH 6.86). It was also discovered that NaCl had the effect of breaking the structure of water in 20% (v/v) EtOH−H2O solution; however, in 60% (v/v) EtOH−H2O solution the same salt at lower concentrations strengthened the water−ethanol structure, promoting the proton exchange between water and ethanol molecules. Hydrogen bond donors as well as acceptors seemed to cause the intimate (or tight) interaction between H2O and EtOH molecules even in alcoholic beverages.

NMR chemical shift study of the methanol—benzene-d6 system

The OH proton chemical shifts of methanol referred to the CH3 proton in the methanol — benzene-d6 system have been measured from room temperature up to the supercritical region. MD simulations have also been performed at the same composition as experiment at 575 K. The chemical shift results in the supercritical region are in good agreement with those of pure methanol at the same density within experimental errors. The results of NMR and MD simulation suggest that the hydrogen-bonded structure of methanol is practically not affected by addition of benzene molecules.

The temperature dependence of the deuterium quadrupole coupling constant and the molecular rotational correlation time in liquid methanol

Temperature dependent experimental measurements of the methanol OH proton chemical shift and the OD deuterium relaxation time for neat methanol were made over the liquid range 200–340 K. From these data values for the deuterium quadrupole coupling constant X D and the molecular rotational correlation time τc, for the OD vector were obtained, X D was found to vary from 196kHz at 200 K to 215 kHz at 340 K, while τc varied from 65.0 ps to 3.0 ps over the same range. Using τc and the liquid viscosity, the size of the supramolecular hydrogen bonded clusters present in the liquid was found to range from 0.25 nm3 at 200 K to 0.24 nm3 at 340 K.

Multinuclear magnetic resonance study of tautomerism in fluorinated β‐diketones

AbstractMultinuclear NMR experiments on fluorinated β‐diketones have furnished information on the various tautomers present in solution and their proportions. 2‐Trifluoroacetyl‐1‐indalone in CDCI3 solution exists in the enol form, as a mixture of exocyclic and endocyclic cis‐enols with the exocyclic form favoured, but in DMF‐d7 solution the equilibrium shifts to 40% enol, 60% hydrate with the enol and hydrate being in slow exchange on the NMR time scale. 2‐Trifluoroacetyl‐1‐tetralone in CDCI3 solution exists only as the enol forms, approximately equally populated, but in DMF‐d7, unlike the indalone, no hydrate is formed although there is now 6% of the keto form present in slow exchange. The experimental results were compared with calculated data produced using molecular orbital simulations. These agree with the NMR results and predict that the tetralone enol tautomers are both significantly populated at room temperature but that the indalone exists primarily as the exocyclic enol. The oxygen‐oxygen internuclear distance in the hydrogen bond was estimated from the OH proton chemical shift based on a calibration from solid‐state data from model compounds, and agrees well with the predictions using the molecular mechanics approach.

Nuclear resonance studies of hydrogen bonding in alcohols: Part 1. Dilution shift studies

The concentration dependence of the OH proton chemical shifts of a variety of alcohols in solution in carbon tetrachloride have been studied by nuclear resonance. The forms of the dilution shift curves obtained and the values of the association shifts have been discussed in relation to the expected extents of hydrogen bonding in such solutions. A limited correlation between the association shifts and the integrated intensities of the OH stretching vibrations of the alcohols studied has been found.