Intramolecular Hydrogen Bonds of the CO…︁H?O Type as Studied by 17O-NMR

The ¹⁷O-NMR spectra of 1,4-naphthoquinone and 5-hydroxy-1,4-naphthoquinone (juglone) have been recorded in CDCl₃ solution at 40°. In juglone the ¹⁷O resonance of the carbonyl peri to the OH group was displaced by 70 ppm to low frequency relative to the resonance in the para-position. It is shown that this chemical shift arises mainly from intramolecular H-bonding, the substituent and steric effects being one order of magnitude smaller. Large carbonyl ¹⁷O chemical shifts between ?34 and ?100 ppm were also observed in a series of aromatic aldehydes and ketones where intramolecular H-bonds of the C?O…?H? O type are formed. The H-bond-induced carbonyl ¹⁷O chemical shifts were linearly correlated with both the ¹⁷O and ¹H chemical shifts of the OH groups. They represent a most sensitive measure of the strength of intramolecular H-bonds. The ¹⁷O resonances of the OH groups were directed to high frequency on H-bonding. Analysis of the ¹⁷O chemical shifts in 2,2′-dihydroxy-benzophenone showed clearly that the two OH groups build H-bonds simultaneously to the single carbonyl group. The ¹⁷O linewidths decreased strongly on H-bonding; the linewidth of the H-bonded carbonyl O-atom in juglone, for example, was reduced by 25% with respect to that of the free carbonyl O-atom. The carbonyl O-atom quadrupole coupling constants in juglone, evaluated from the combined use of ¹³C and ¹⁷O relaxation times, were 9.5 and 11.0 MHz, respectively. No correlation was observed between the H-bond-induced ¹⁷O chemical shifts and the variations in ¹⁷O quadrupole coupling constants.     

17O NMR investigation of p,π-interactions in α,β-unsaturated and aromatic ethers

The ¹⁷O chemical shifts have been measured for 51 α,β-unsaturated and aromatic ethers. A good linear relationship is found between the ¹⁷O chemical shifts in a series of dialkyl and the corresponding alkyl vinyl ethers. Hence, the extent of p,π-interaction, between the oxygen atom and the vinyl group in the latter series does not, apparently, depend upon branching at the α-carbon atom in the alkyl moiety of these ethers. The PhOBu^t ether, however, as compared to the other alkyl phenyl ethers, shows significantly weakened p,π-interaction, which is apparently related to the steric hindrance of this interaction. The effects of two unsaturated groups upon the ¹⁷O chemical shifts in the corresponding ethers are non-additive. This is undoubtedly a result of ‘rivalry’ between these groups for conjugation with the lone electron pairs on the ethereal oxygen. The ¹⁷O chemical shift ranges of substituted methyl and vinyl phenyl ethers are nearly equal (≈30 ppm). An analysis of the ¹⁷O shielding for cyclopropyl ethers shows no observable p,σ-conjugation in these compounds. Excellent correlation (r>0.99) between the values of ¹⁷O chemical shifts and the calculated (MO LCAO SCF, CNDO/2) π-electron charges on the corresponding oxygen atoms look promising for experimental estimations of π-electron densities on the ethereal oxygen.     

Photocatalytic direct oxygen-isotopic labelings of carbonyls in ketones and aldehydes with oxygen-isotopic waters

Oxygen-isotopic labelings play important roles in identifying and understanding chemical and biological processes. Direct C=O to C=¹⁸O or C=¹⁷O conversion in a single step leading to labeled compounds can alleviate synthetic burdens without the need for resynthesis. Here we describe a photocatalytic oxygen-isotopic labeling protocol that can efficiently and selectively install ¹⁸O and ¹⁷O on carbonyls of ketones and aldehydes via oxygen isotope exchange with oxygen-isotopic waters (H₂¹⁸O or H₂¹⁷O) as the sources of oxygen isotopes, in which light and oxygen-enabled sodium alkanesulfinates catalyzed this process. This strategy was extended to the in-situ formed ketones from the photocatalytic aerobic oxidation of alkyl arenes and secondary alcohols. Furthermore, reduction of the oxygen-isotopically labeled aldehydes with NaBH₄ provided the corresponding oxygen-isotopically labeled primary alcohols. We believe that the oxygen-isotopically labeling method will be widely used in chemistry, biology and medicine fields.     

Résonance Magnétique Nucléaire de 17O. Aldéhydes et cétones aliphatiques: additivité des effets de substitution et corrélation avec la 13C-RMN

¹⁷O-NMR. Aliphatic aldehydes and ketones, additivity of substituent effects and correlation with ¹³C-NMR. The ¹⁷O-chemical shifts of 9 aldehydes, 22 aliphatic and 4 alicyclic ketones, in the natural abundance FT.-NMR. spectra followed a good correlation with the ¹³C-chemical shifts of the terminal C-atoms of corresponding methylene compounds. An additivity relation involving 6 parameters represents the ¹⁷O-shifts of 28 of the measured products with a standard deviation of 2.5 ppm. The additivity parameters are discussed with respect to the modifications of the polarity of the carbonyl group induced by the hyperconjugative interaction of π and π* orbitals with the πCH ₃ orbitals of the alkyl substituent groups.     

Bor-Stickstoff-Verbindungen,LXVIII [1]. Kernresonanzspektroskopische Untersuchungen an 1,3,2-Diazaboracycloalkanen und Phenylboranderivaten

Boron-Nitrogen Compounds. LXVIII. Nuclear Magnetic Resonance Studies on 1,3,2-Diazaboracyloalkanes and Phenylborane Derivatives The ¹H chemical shift differences Δδ = δ (NCH ₂) – δ (NCH ₃) of 1,3-dimethyl1,3,2-diazaboracycloalkanes as well as the corresponding differences of ¹³C chemical shifts are dependent upon the ring size. No simple correlation exists between δ_11B and δ_13C of the boron-bonded phenyl carbon atom of phenylborane derivates, although stereochemical factors appear to influence the absolute values of δ_13C. ¹³C Nuclear resonance measurements permit the observation of conformational isomers of bis(methylamino)phenylborane and N-trimethyl-B-triphenylborazine at low temperatures and confirm the pseudoarmatic nature of the 1,3,2-diazaboroline ring system.     

17O-enriched α-azohydroperoxides: 17O NMR spectroscopy, 17O-labeling reagents

¹⁷O-enriched α-azohydroperoxides, prepared by autoxidation, are efficient ¹⁷O-labeling reagents; ¹⁷O NMR (CD₃CN) of 2 showed broad signals at δ 254 and 204 PPM; the solvent dependence of the ¹⁷O chemical shifts and the kinetics of ionic oxidations are interrelated.     

Carbon-13 NMR spectra of a series of para-substituted N,N-dimethylbenzamides. Comparisons of linear free energy relationships for carbon-13 and nitrogen-15 chemical shifts and rotation barriers

All carbon-13 chemical shifts for 11 para-substituted N,N-dimethylbenzamides in 1 mole % chloroform solution are reported, with assignments based upon double resonance experiments, analogy to chemical shifts of benzamide, and self-consistency between experimental and calculated values using recognized substituent parameters. In contrast to earlier reports, the aryl carbon chemical shift assignments for N,N-dimethylbenzamide are C-2, 127.0; C-3, 128.7; C-4, 129.4, and for p-chloro-N,N-dimethylbenzamide are C-1, 134.6; C-4, 135.5 ppm, relative to internal TMS. Good Hammett correlations (σ_p) are reported for ¹³C chemical shifts of C-1 (σ = 11.9 ppm) and even for the carbonyl group (σ = ?2.3 ppm) but are markedly improved if correlated with σ_p+ (σ = 9.5 ppm) and Dewar's F (σ = ?1.9 ppm), respectively. Excellent Swain–Lupton F and R correlations were found for some of the ¹³C chemical shifts and yielded values for percent resonance contributions to transmission of substituent effects as follows, C-1, 75 ± 4%; C-2, 51 ± 3%; C?O, 31±2%. These are compared to similar values calculated from the C?O of benzoic acids of 34±10%, and from the nitrogen-15 chemical shifts of benzamides of 56±2%. Correlations of these ¹³C δ values and ¹⁵N δ values with rotation barriers (ΔG) for N,N-dimethylbenzamides were examined, and it was found that while C?O δ values correlated only poorly the C-1 δ values correlated very well, but the best correlation was for ¹⁵N δ values of benzamides. It is suggested that Δ G and δ ¹⁵N are intrinsically related due to their numerical correlation, and the close similarity in percent resonance contribution of substituent influence on these parameters.     

Ab initio MO calculations and 17O NMR at natural abundance of para-substituted acetophenones

¹⁷O NMR chemical shifts and calculated (ab initio MO theory) electron densities are reported for a series of para-substituted acetophenones, X? C₄H₆? COCH₃, where X = NH₂, OCH₃, F, Cl, CH₃, H, COCH₃, CN, NO₂. The ¹⁷O shifts are very sensitive to the para substituent and cover a range of some 51 ppm. Donors induce upfield shifts and acceptors downfield shifts. The substituent chemical shifts (SCS) correlate precisely with σ_I and σ_R⁺ using the Dual Substituent Parameter (DSP) method. The derived transmission coefficients ρ_I and ρ_R indicate that polar and resonance mechanisms contribute approximately equally to the observed substituent effects. The shifts also correlate well with calculated π-electron densities (slope = 1500 ppm per electron) confirming their electronic origin. λ values are also reported, and the role of the average excitation energy, ΔE, in determining ¹⁷O SCS values is discussed. It is concluded that variations in ΔE are minor and that the local Δ-electron density is the dominant feature controlling ¹⁷O SCS values.     

17O, 13C and 1H NMR and IR spectral study of crowded ketones: possible intramolecular C—H···O interactions

Unusual behaviour was observed in the study of the ¹⁷O, ¹³C and ¹H NMR and IR spectra of crowded (1‐adamantyl)alkyl ketones. As the size of the alkyl substituent is increased, abnormal upfield chemical shifts in the ¹³C NMR and downfield shifts in the ¹⁷O NMR of the carbonyl group, as well as downfield shifts in the ¹H NMR of the adamantyl γ'‐protons, are found. In the IR spectrum, the ν_C?O stretching frequencies of the ketones with bulky substituents show considerable red shifts. Correlation of the NMR shifts with the number of γ‐carbon atoms of the alkyl substituents and comparison with the IR results indicated that there is an intramolecular through‐space CH···O interaction in crowded ketones. This was supported by the results of ab initio calculations. Copyright © 2002 John Wiley & Sons, Ltd.     

A contradistinction in the magnetic (13C NMR spectroscopy) and chemical behaviour of 4-Oxo-4,5,6,7-tetrahydroindole derivatives

Carbon-13 NMR data are reported for a series of 1,2-diaryl-4-oxo-4,5,6,7-tetrahydroindoles, 6-methyl-2-phenyl-4-oxo-4,5,6,7-tetrahydrobenzofuran and 1-,6-dithiaindan-4-one. The chemical shifts δ 193–196, δ 195.5 and δ 184 are identified for the carbonyl carbon (C-4) in the tetrahydroindoles, tetrahydrobenzofuran and dithiaindan derivatives, respectively. These shifts are located in the same region as that reported for the corresponding carbonyl carbon in aryl conjugated ketones. An excellent correlation between the chemical shift for the carbonyl carbon and the chemical reactivity of the ketonic function is noticed in the case of the latter two series of ketones while such a correlation is typically absent in the case of the 4-ketotetrahydroindole derivatives.     

17O, 13C, 1H NMR and IR spectroscopic investigations of (CH3)nC5H5–nRe(CO)3 analogues (n = 0–5)

¹³C, ¹H NMR investigation of the (CH_3nC₅H_5–nRe(CO)₃ Me_nCpReT) n = 0–5 analogous series showed that the signals of almost all magnetic nuclei shift upfield with increase n, which also occurs in (Me_nCp)₂M compounds (M = Fe²⁺, Co³⁺; n = 0–5). The smaller value of the C(CH₃) signal (1.5 ppm.) shifts upfield when a further methyl group is introduced into the vicinal position, this shift can be attributed to the absence of the second methyl cyclopentadienyl ring. It is noteworthy that methyl cyclopentadienyl ring coordination to the transition-metal atom results in the downfield shift of the substituted carbon atom (C_key) signal. One of the reasons for such a shift might be the reduction in screening effect of the central CpM bond π-electron current on C_key owing to nodal properties of Cp ring e-orbitals. The δ ¹³C(CO), δ ¹⁷O(CO), and v(CO) values reflect successive increases of Re → CO π-back donation with increase in n.     

Saturated amine oxides: part 10. hydroacridines: part 32. linear 17O/13C and 13C/13C chemical shift correlations between saturated azaheterocyclic N‐methylamine N‐oxides,and the methiodides of their parent amines

Two kinds of good linear correlations were found between the chemical shifts of saturated six‐membered azaheterocyclic N‐methylamine N‐oxides and the chemical shifts of the methiodides of their parent amines. One of the correlations occurs between the ¹⁷O chemical shift of the N⁺―O^– oxygen in the N‐oxides and the ¹³C chemical shift of the N⁺―CH₃ methyl group analogously situated in the appropriate methiodide (r = 0.9778). This correlation enables unambiguous configuration assignment of the N⁺―O^– bond, even if the experimentally observed ¹⁷O chemical shift of only one N‐epimer is available, provided the ¹³C chemical shifts of both N⁺―CH₃ groups in the methiodide are known and assigned; furthermore, it can be used also for the estimation of ¹⁷O chemical shifts of the N⁺―O^– oxygens in N‐epimeric pairs of N‐oxides, for which observed ¹⁷O data hardly become available. The second correlation is observed between the ¹³C chemical shift of the N⁺―CH₃ methyl group in the N‐oxides and the ¹³C chemical shift of the N⁺―CH₃ methyl group analogously situated in the appropriate methiodide (r = 0.9785). It can be used for safe configuration assignment of the N⁺―CH₃ group and, indirectly, also of the N⁺―O^– bond in an amine N‐oxide, even if no ¹⁷O NMR data, and the ¹³C chemical shift of only one N‐epimer is available. Copyright © 2015 John Wiley & Sons, Ltd.     

Chemical shift correlations in the 13C, 17O and 31P NMR spectra of some Mo(CO)4((PPh2O)2Y(R)R′) (Y(R) = P(O), Si(Me); R′ = alkyl,haloalkyl, aryl) and [Mo(CO)4(PPh2O)2]2Si complexes

The syntheses and ¹³C, ¹⁷O, ²⁹Si and ³¹P NMR spectra of a series of Mo(CO)₄((PPh₂O)₂Y(R)R′) (Y(R) = P(O), Si(Me); R′=alkyl, haloalkyl, aryl) and [Mo(CO)₄(PPh₂O)₂]₂Si complexes are given. The chemical shift ranges of the cis and trans carbonyl ¹³C and ¹⁷O, phenyl C(1) ¹³C and ³¹P resonances are relatively large and, with the exception of the cis carbonyl ¹⁷O chemical shifts, the correlations between the chemical shifts of the various resonances are excellent. These correlations are consistent with the model of metal carbonyl ¹³C and ¹⁷O chemical shifts proposed by Bodner and Todd. In addition they allow the model to be extended to include the diphenylphosphinite ³¹P chemical shifts in these complexes. The excellent correlations may be due to the presence of the chelate ring which limits the rotation around the molybdenum-phosphorus bond and to the fact that all three groups directly bonded to the phosphorus remains constant.     

Analysis of ;W and O NMR chemical shifts in polyoxometalates by extended Hückel mo calculations

The extended Hückel molecular orbital (EHMO) calculations have been carried out using cluster approach to polyoxo anions, i.e. calculations have been done for a single octahedron MO₆ of different symmetry and results have been used to analyze ¹⁸³ W and ¹⁷ O NMR spectra. Using five d→d* energy differences for the individual WO₆ the sum Σ1/ (E_d→E_d*) have been calculated and plotted against the ¹⁸³ W chemical shift (from +258 to −670 ppm) for corresponding type of tungsten atom and practically a linear correlation between two parameters have been observed. This points out the electronic nature of the ¹⁸³ W chemical shift. Similar correlation have been found for the ¹⁷O NMR chemical shifts (−90 to +800 ppm) when the plotted against product of the R⁻³ Σ1/ (E_p→E_p*) where the R⁻³ bond length of the corresponding W–O bond. Increasing the ¹⁸³ W nuclear magnetic shielding with the calculated electron population on tungsten atom for closely related anions has been observed, but no general tendency between δ and the calculated electronic charge if the symmetry of polyhedron is changed is expected.     

17O NMR studies on polycyclic quinones,hydroxyquinones and related cyclic ketones: Models for anthracycline intercalators

The ¹⁷O chemical shifts for six cyclic ketones which serve as models for quinones, viz. cyclohex-2-enone (1), α-tetralone (2), anthrone (3), 4H-pyran-4-one (4), 1-benzopyran-4(4H)-one (5), xanth-9-enone (6), and for six quinones, viz. benzoquinone, naphthoquinone, anthraquinone, 2,5-dihydroxybenzoquinone 5,8-dihydroxynaphthoquinone and 1,4-dihydroxyanthraquinone, were measured in toluene at 90°C. A shielding effect of approximately 50 ppm per fused benzene ring was noted for the quinones and related carbocyclic ketones; however, the analogous series of heterocyclic fused ring ketones 4–6 showed only a slight fused-ring effect on the carbonyl chemical shift. A single ¹⁷O resonance was observed for 2,5-dihydroxybenzoquinone (358 ppm) and 5,8-dihydroxynaphthoquinone (283 ppm), indicating rapid proton exchange between the oxygen atoms of these compounds. However, 1,4-dihydroxyanthraquinone gave two discrete ¹⁷O signals at 441 and 87 ppm, indicating that in this case proton exchange between oxygen atoms is slow.     

17O NMR spectra of equatorial and axial hydroxycyclohexanes and 5-hydroxy-1,3-dioxanes and their methyl ethers

¹⁷O chemical shifts of axial hydroxyl groups in cyclohexanols are upfield of those of corresponding equatorial groups, but in 5-hydroxy-1,3-dioxanes the opposite is observed: the axial OH resonates downfield of the equatorial OH. The situation is the same in the corresponding methyl ethers and is, thus, not a result of intramolecular hydrogen bonding in the axial 5-hydroxy-1,3-dioxane, but appears to parallel the effect on ¹³C and ¹⁹F shifts observed in corresponding equatorial and axial 5-methyl- and 5-fluoro-1,3-dioxanes, which has been attributed to an upfield shifting effect of the antiperiplanar γ-located heteroatoms. Surprisingly, the reciprocal effect is not seen in the ring ¹⁷O shifts of the 5-hydroxy-1,3-dioxanes. A δ compression shift is seen in the ¹⁷O spectrum of trans-3,3,5-trimethylcyclohexanol (syn-axial OH and CH₃), analogous to the effect earlier reported in ¹³C spectra. Conversion of four of the alcohols to methyl ethers produces a large upfield effect on the ¹⁷O shift, larger in the cyclohexanols than in the 1,3-dioxane-5-ols. Similar upfield shifts have been recorded in the literature; their extent depends on whether the alcohols are primary, secondary or tertiary.     

15N chemical shifts in aziridines

For a number of 1-substituted aziridines and also some 1,2-disubstituted aziridines it has been shown that electron-donating substituents on the nitrogen atom produce a downfield shift of the ¹⁵N resonance. The ¹⁵N chemical shifts of aziridines correlate with the ¹⁵N shifts in N,N-dimethylamines and primary amines as well as with the ¹⁷O shifts in oxiranes. A correlation is also observed between the ¹⁵N chemical shifts and the electronegativity of the substituents on the nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, 1336–1339, October, 1988.     

Reactions with Hydrophosphoryl Halides

Abstract

In the systems RPCl₂+H₂O, RPCl₂+RCOOH, RPCl₂+RPH(O)OH and RPH(O)OH+RCOX the formation of hydrophosphoryl halides RPH(O)X (X=Cl,Br,I; R=H,OH,Hal,Alk,AlkO,Ar) was proved by spectral and chemical methods. Hydrophosphoryl halides react with alyphatic ketones R′₂CO yielding phosphinic halides R[R′₂C(OH)]P(O)X (X-ray analysis). In case of aromatic aldehydes and ketones containing electron donor substituentes, the addition products are rearranged into α-halogenalkylphosphinic acids.     

Correlations of 95Mo NMR chemical shifts with ligand basicity in substituted pyridine pentacarbonylmolybdenum(O) complexes

Molybdenum-95 NMR chemical shifts are reported for a series of Mo(O) compounds of the type Mo(CO)₅L (L = pyridine derivatives). A good correlation is found between the δ(⁹⁵Mo) values and the Hammett sigma constant of the pyridine substituent or the pK_a of the substituted pyridine. The chemical shift values, which range from −1366 ppm (3-CN, σ = 0.62, pK_a = 1.35) to −1433 ppm (4-NMe₂, σ = −0.83, pK_a = 9.61), directly reflect the electronic properties of the pyridine derivatives even though the substituent is four or five bonds away from the molybdenum atom.     

Résonance magnétique nucléaire de 13C et 17O d'éthers aliphatiques. Effets γ entre les atomes d'oxygène et de carbone

The ¹³C- and ¹⁷O-chemical shifts of 31 aliphatic ethers are measured and discussed. The ¹⁷O-chemical shifts of the ethers ROR′ correlate with chemical shifts for the methylene groups of the corresponding alkanes RCH₂R′. The constant of proportionality can be related to the orbital expansion term 〈r^?3〉_2p. The δ_c for carbon atoms can also be correlated with δ_c for the corresponding alkanes. The origin of the correlation is discussed taking into account the conformational modifications resulting from introduction of an oxygen atom in an alkyl chain.