1H and 13C NMR study of 8-hydroxyquinoline and some of its 5-substituted analogues

¹H and ¹³C NMR spectra of 8-hydroxyquinoline (oxine) and its 5-Me, 5-F, 5-Cl, 5-Br and 5-NO₂ derivatives have been studied in DMSO-d₆ solution. The ¹H and ¹³C chemical shifts and proton–proton, proton–fluorine, carbon–proton and carbon–fluorine coupling constants have been determined. The ¹H and ¹³C chemical shifts have been correlated with the charge densities on the hydrogen and carbon atoms calculated by the CNDO/2 method. The correlation of the ¹H and ¹³C chemical shifts with the total charge densities on the carbon atoms is approximately linear (r_H² = 0.85, r_C² = 0.84). The proton in peri position to the nitro group in 5-NO₂-oxine is an exception.     

Characterization of tri-o-methylcellulose by one- and two-dimensional NMR methods

Tri-O-methylcellulose was prepared from partially O-methylated cellulose and its chemical shifts (¹H and ¹³C), and proton coupling constants were assigned using the following NMR methods: (1) One-dimensional ¹H and ¹³C spectra of the title compound were used to assign functional groups and to compare with literature data; (2) double quantum filtered proton–proton correlation spectroscopy (¹H, ¹H DQF-COSY) was used to assign the chemical shifts of the network of 7 protons in the anhydroglucose portion of the repeat unit; (3) the heteronuclear single-quantum coherence (HSQC) spectrum was used to establish connectivities between the bonded protons and carbons; (4) the heteronuclear multiple-bond correlation (HMBC) spectrum was used to connect the hydrogens of the methyl ethers to their respective sugar carbons; (5) the combination of HSQC and HMBC spectra was used to assign the ¹³C shifts of the methyl ethers; (6) all spectra were used in combination to verify the assigned chemical shifts; (7) first-order proton coupling constants data (J_H,H in Hz) were obtained from the resolution-enhanced proton spectra. The NMR spectra of tri-O-methylcellulose and other cellulose ethers do not resemble the spectra of similarly substituted cellobioses. Although the ¹H and ¹³C shifts and coupling constants of 2,3,6-tri-O-methylcellulose closely resemble those of methyl tetra-O-methyl-β-D -glucoside, there are differences with regard to the chemical shifts and the order of appearances of the resonating nuclei of the methyl ether appendages and the proton at position 4 in the pyranose ring. H4 in tri-O-methylcellulose is deshielded by the acetal system comprising the β-1→4 linkage, and it resonates downfield. H4 in the permethylated glucoside is not as deshielded by the equitorial O-methyl group at C4, and it resonates upfield. The order of appearance of the ¹H and ¹³C resonances in the spectra of the tri-O-methylcellulose repeat unit (from upfield to downfield) are H2 < H3 < H5 < H6a < H3a < H2a < pro R H6B < H4 < pro S H6A ≪ H1 and C6a < C3a < C2a < C6 < C5 < C4 < C2 < C3 ≪ C1, respectively. Close examination of the pyranose ring coupling constants of the repeat unit in tri-O-methylcellulose supports the ⁴C₁ arrangement of the glucopyranose ring. Examination of the proton coupling constants about the C5-C6 bond (J_5,6A and J_5,6B) in the nuclear Overhauser effect difference spectra revealed that the C6 O-methyl group is predominantly in the gauche gauche conformation about the C5-C6 bond for the polymer in solution. © 1999 John Wiley & Sons, Inc.* J Polym Sci A: Polym Chem 37: 4019–4032, 1999     

Group IV organometal derivatives of pyridine. I—A 1H and 13C NMR investigation of trialkylmetal derivatives of pyridine

The proton and carbon-13 NMR spectra of thirteen trialkylmetal derivatives of pyridine, several of which were previously unknown, have been recorded and analysed. The proton NMR spectra show variations in proton chemical shifts but not in proton-proton coupling constants when the metal substituent is changed; the ring proton-metal coupling constants ⁿJ(M? H) in the tin and lead derivatives correspond closely with the corresponding proton-proton couplings ⁿJ(H? H) in pyridine. The carbon-13 chemical shifts of the carbons bound to the metal can apparently be correlated with the electron-donating ability of the trialkylmetal group. In the trimethylstannylpyridines the value of ¹J(Sn? C_ring) varies greatly with the position of the Me₃Sn group.     

Pulsed fourier transform NMR of substituted aryltrimethyltin derivatives : III. Proton data at 100 MHz and the derived Hammett σ-constant of the trimethyltin group

Proton NMR data at 100 MHz are reported for thirteen para- and meta-substituted phenyltrimethyltin compounds, XC₆H₄Sn(CH₃)₃, where X = para-N(CH₃)₂, para-OCH₃, para-OC₂H₅, para-CH₃, meta-CH₃, -H, para-F, meta-OCH₃, para-Cl, para-Br, meta-F, meta-Cl and para-Sn(CH₃)₃. Correlation coefficients with Hammett σ-constants of greater than 0.95 are obtained with the methyltin proton chemical shifts and coupling constants to carbon [¹J(¹³C¹H)] and tin [²J(SnC¹H)]. Solvent effects and other extraneous factors invalidate comparisons of ? values in terms of the relative attenuation of the transmission of substituent effects through homologous carbon, silicon, germanium and tin systems, but coupling constant data reflect a diminution of ca. one tenthfold per bond in the order ?[C(1)Sn] > ? [SnC] > ? [CH]. Satisfactory correlations (r > 0.95) are obtained in this series of closely-related compounds among the conventionally recorded two-bond, ²J(SnC¹H) and the constituent, one-bond ¹J (Sn¹³C) and J(¹³C¹H) coupling constants, but the correlation coefficient for the comparison between the two one-bond couplings, ¹J(Sn¹³C) and ¹J(¹³C¹H) is lower (r = 0.872). Changes in the couplings at the methyltin carbon bond tin-119 atoms are interpreted in terms of isovalent hybridization; a model based upon effective nuclear charges is tested with respect to both NMR coupling constants and ¹¹⁹Sn Mössbauer Isomer shifts at tin and is invalidated. Proton and carbon-13 NMR, chemical shift and coupling constant data are used to derive a Hammett σ-constant for the para-trimethyltin group of ?0.14, and the significance of this value is discussed.     

Deuterium-isotopieeffekte auf die 13C-chemischen verschiebungen und kohlenstoff-deuterium kopplungskonstanten in deuterierten verbindungen

The isotope effects on the ¹³C NMR chemical shifts and coupling constants (¹³C¹H and ¹³C¹H) have been determined by pulse Fourier transform ¹³C NMR investigation at 22·63 MHz for more than 30 common deuterated and protonated solvents. The observed isotope effects correlate with hybridization and electron withdrawal at the coupling carbon within the series of comparable compounds. In agreement with MO-theoretical calculations a linear correlation between the J_CD values of CD_x groups and the J_CH values of the corresponding CH_x groups was found. The experimentally determined J_CD values show an average deviation from the calculated line J_CD = (γ_D/γ_H)J_CH = 0·154 ×J_CH on the order of± 1 Hz.     

13C-NMR-spektren von di- und trinuclearen polymethincyanin-farbstoffen

¹³C NMR chemical shifts are reported and assigned for two vinylogous series of polymethinecyanine dyes with indolenine- and benzothiazole nuclei. The influence of the heterocyclic groups and the chain length upon the chemical shifts of the methine carbons and upon the corresponding ¹J_¹³C¹H-coupling constants has been studied. ¹³C chemical shifts of indolenine derivatives correlate with calculated π-electron densities. The combined application of ¹H- and ¹³C NMR spectroscopy turns out to be a useful method for detecting steric hindrance in polymethine dyes.     

13C-NMR-Spektren von Cyclopropenen und Benzocyclopropenen

The substituent parameters of methyl-, halogen-, methoxycarbonyl- and phenyl-substituted cyclopropenes as well as of cyclopropenone and diphenylcyclopropenone are determined from the ¹³C chemical shifts. The influence of the carbonyl group on the chemical shifts and charge densities is studied in the cyclopropenones. The interaction between the cyclopropene nucleus and the annulated benzene ring in benzocyclopropenes is evaluated with the aid of the ¹³C NMR spectra of di- and tetraphenyl-substituted benzocyclopropene derivatives and of dimethyl 1H-cyclopropa[a]naphthalene-1,1-dicarboxylate. The J values are shown to be better indicators of structural changes than the δ values. α-Effects of substituents give a good correlation with Hammett σ₁-values.     

The 13C,H coupling constants in structural and conformational analysis. III.. Long-range carbon–hydroxyl proton couplings as evidence of hydrogen bonding in some acylphloroglucinols

Proton coupled ¹³C NMR spectra have been recorded for some acylphloroglucinol derivatives. Significant couplings over two, three and four bonds were observed between the hydroxyl proton and aromatic carbons for those compounds where the hydroxyl group is hydrogen bonded strongly enough to the carbonyl carbon of the acyl side chain. Typical values were ²J = 4.8 Hz, and ³J = 5.6 Hz or 6.7 Hz corresponding to dihedral angles of c. 0° and c. 180°, respectively; the dihedral angle is defined as the angle between the O—H bond and the plane of the aromatic ring. A stereospecific ⁴J(COH) value of 1.2 Hz for a ‘W’ arrangement of coupled atoms was also found. An interesting example of ‘virtual’ J(CH) coupling was observed in the proton coupled spectrum of 1-butyrylphloroglucinol 2-monomethyl ether in acetone-d₆ caused by the accidentally equal chemical shifts of the two ring protons.     

Carbon-13 nuclear magnetic resonance studies of creatine,creatinine and some of their analogs

Creatine (N-methyl-N-amidinoglycine), creatinine (1-methyl-2-aminoimidazolin-4-one) and a series of 38 of their close structural analogs have been examined using natural abundance ¹³C NMR spectroscopy at 25.16 MHz. Both proton-coupled and proton noise-decoupled spectra were recorded. Unequivocal assignments of the carbon resonances could be made in the vast majority of cases. Both ¹³C NMR chemical shifts and ¹J(CH) values can be used to characterize and to differentiate readily between analogs of creatine and analogs of creatinine. For example, the ¹J(CH) coupling constants for the α-carbons of the acyclic creatine analogs were all in the 140–142 Hz range, whereas the corresponding coupling constants for the related, cyclized creatinine analogs were all in the 150–152 Hz range.     

Natural abundance 13C NMR investigation of substituted bromobenzene using noise decoupling of proton resonances

The natural abundance ¹³C NMR spectra of bromobenzene and ten derivatives have been obtained using the technique of noise modulated decoupling of the proton resonances. Assignments have been made for all ¹³C resonance signals using an additivity rule. The chemical shifts of the aromatic carbon nuclei in the para-substituted compounds are discussed in terms of the Taft parameters (σ_R, σ_I) and the electronegativity of the substituent.     

15N, 31P,and 13C NMR Spectroscopy of N-Arylsulfonyl-and N-Arylcarbonyl-P,P,P-triphenylphospha-λ-Azenes. Substituent Effects and Electronic Structure

Abstract

The ¹⁵N, ³¹P and ³¹C NMR spectra of several series of phospha-λ⁵-azenes are reported. For the N-arylsulfonyl-P,P,P-triphenylphospha-δ⁵-azene series (R-C₆H₄N-SO₂-PPh₃), the ³¹P chemical shifts, various ¹³C chemical shifts and ¹J_PN were observed to correlate linearly with the Hammett σ constants. Interestingly, the ¹⁵N chemical shifts did not correlate acceptably with any σ or with the Taft dual substituent parameter equation, and 1J_PC was invariant with substituent. For the N-arylcarbonyl-P,P,P-triphenylphospha-λ⁵-azene series (R-C₆H₄-CO-N=PPh₃), δ_31P and various δ_13C's were observed to linearly correlate with the δ constants, while δ_15N, ¹J_PN and ¹J_PC correlated with both the σ and σ constants. For the N-phenyl-P,P,P-triarylphospha-λ⁵-azene series [Ph-N=P(C₆H₄-R)₃] the best correlations were observed between ³¹P, ¹⁵N and several ¹³C chemical shifts and the σ constants.     

The study of longifolene by two-dimensional NMR spectroscopy

The complete assignment of the ¹³C NMR spectrum of longifolene was achieved from double quantum coherence measurements, while combined evaluation of a ¹H? ¹³C heteronuclear chemical shift correlation diagram and a homonuclear ¹H J-resolved diagram provided all proton chemical shifts. Conformational information on the seven-membered ring of the tricyclic sesquiterpene was obtained from proton chemical shift considerations.     

Etude par Résonance Magnétique Nucléaire du carbone 13 de complexes du cobalt (III) et de la diméthylglyoxime

From a carbon magnetic resonance study of several alkylcobaloximes RCo(DMG)₂B (DMG = dimethylglyoximate monoanion), it was possible to estimate the α, β and γ effects of the Co(DMG)₂B group on the chemical shifts of the carbon atoms of various alkyl groups R. The chemical shifts of the carbon atoms belonging to the equatorial ligands and to the axial base B are not significantly affected by structural modification of the R groups. Values of δ in benzylcobaloximes XC₆H₄CH₂Co(DMG)₂B agree with a donor effect of the ? CH₂Co(DMG)₂B radical. Values of ¹J(¹³C? H) coupling constants, measured in ¹³C enriched methylcobaloximes, do not vary appreciably when B is changed (J(¹³C? H) = 137 ± 1 Hz) and are close to the value obtained for methylcobalamine.     

Estimation and prediction of 13C NMR chemical shifts of carbon atoms in both alcohols and thiols

Quantitative structure-spectrum relationship calculations of ¹³C NMR chemical shifts of both 302 carbon atoms in 56 alcohols and 62 carbon atoms in 15 thiols are described using several parameters: the atomic ionicity index (INI), the polarizability effect index (PEI), and stereoscopic effect parameters (?) of the compounds. The ¹³C NMR chemical shifts for these compounds of both alcohols and thiols can be estimated through the multiple linear regression (MLR). A MLR model was built with variable screening by the stepwise multiple regression and examined by validation on its stability. The correlation coefficient of the established model as well as the leave-one-out cross-validation was 0.9724 and 0.9716 respectively. The results obviously indicate that INI and ? are linearly related with ¹³C NMR chemical shifts, which provides a new method for calculating ¹³C NMR chemical shifts in the compounds of both alcohols and thiols.     

Studies in tertiary amine oxides part II—carbon-13 nuclear magnetic resonance spectra of selected acetylenic amines,their N-oxides and the Meisenheimer rearrangement products

Carbon-13 NMR chemical shifts and ¹J(CH), ²J(CH) and ³J(CH) coupling constants of selected saturated nitrogen heterocyclic molecules containing the acetylenic moiety have been determined. These NMR parameters have also been determined for the corresponding N-oxides and the Meisenheimer rearrangement products, the O-allenylhydroxylamines. The effect of the N-oxidation on the chemical shifts of the ring and the acetylenic carbon atoms is discussed.     

Etude de divers types de diastereotopie par RMN de 1H et de 13C dans les series du ferrocene et du titanocene

The influence of a chiral group on the ¹H and ¹³C NMR parameters of ferrocenes and titanocenes is studied. The difference of screening due to the diastereotopy of the cyclopentadienyl carbon nuclei is usually larger than the non-equivalence of corresponding proton chemical shifts. If the chiral group is the titanium atom itself a diastereotopy is also introduced into the cyclopentadienyl ring. Proton spectra obtained at 250 MHz, INDOR and off-resonance experiments, using chemical shift reagents permit a complete analysis of the proton and carbon spectra of some derivatives, especially ferrocene with a CH(CH₃)(CH₂CO bridge and titanocene with a CH(CH₃)CH₂CH₂ bridge. The result give information on the stereochemistry, and preferred conformations are identified.     

1H NMR parameters of the N-terminal 13-residue C-peptide of ribonuclease in aqueous solution

The ¹H NMR chemical shifts and the spin-spin coupling constants of the non-exchangeable protons of the N-terminal 13-residue C-peptide of ribonuclease A, obtained by cleavage of the enzyme with cyanogen bromide, have been measured in a 5 mM solution in D₂O (pH 3.0, 24°C) at 360 MHz. The titration parameters for end groups (Lys-1 and homo-Ser-13) and side chains (Lys-1, Glu-2, Lys-7, Glu-9 and His-12) have been determined. The chemical shifts, their temperature coefficients and the vicinal coupling constants, ³J(HNCH-α), for the exchangeable NH protons have been measured in a 5 mM solution in D₂O/H₂O (1:9 v/v) at pH 3.0. An assignment of observed signals to individual residue protons based on characteristic shifts, standard double resonance experiments, spectral simulations and titration shifts is proposed. All experimental evidence indicates that under the conditions studied the C-peptide is in a random coil form.     

A set of triple-resonance nuclear magnetic resonance experiments for structural characterization of organophosphorus compounds in mixture samples

The ¹H, ¹³C correlation NMR spectroscopy utilizes J_CH couplings in molecules, and provides important structural information from small organic molecules in the form of carbon chemical shifts and carbon-proton connectivities. The full potential of the ¹H, ¹³C correlation NMR spectroscopy has not been realized in the Chemical Weapons Convention (CWC) related verification analyses due to the sample matrix, which usually contains a high amount of non-related compounds obscuring the correlations of the relevant compounds. Here, the results of the application of ¹H, ¹³C, ³¹P triple-resonance NMR spectroscopy in characterization of OP compounds related to the CWC are presented. With a set of two-dimensional triple-resonance experiments the J_HP, J_CH and J_PC couplings are utilized to map the connectivities of the atoms in OP compounds and to extract the carbon chemical shift information. With the use of the proposed pulse sequences the correlations from the OP compounds can be recorded without significant artifacts from the non-OP compound impurities in the sample. Further selectivity of the observed correlations is achieved with the application of phosphorus band-selective pulse in the pulse sequences to assist the analysis of multiple OP compounds in mixture samples. The use of the triple-resonance experiments in the analysis of a complex sample is shown with a test mixture containing typical scheduled OP compounds, including the characteristic degradation products of nerve agents sarin, soman, and VX. The viability of the approach in verification analysis is demonstrated in the analysis of the 30th OPCW Proficiency Test sample.     

Carbon-13 nuclear magnetic resonance spectroscopy—VII:para-substituted fluorobenzenes

C-13 and F-19 NMR spectra of seventeen para-substituted fluorobenzenes were measured and the chemical shifts as well as coupling constants with respect to substituents were analysed. The chemical shifts of the fluorine, the C₁ and the C₂ atoms were found to depend on the total electron densities. In the case of the C₃ atom, the chemical shifts seem to depend on π-electron densities rather than the total electron densities. The present calculations also indicate that the chemical shift of the C₄ atom depends mainly on σ-electron densities due to the inductive effects of substituents. The strongest factor influencing the coupling constant, ⁿJ(C? F), is also considered to be the π-electron densities on the carbon atoms. In the case of the direct couplings, ¹J(C? F), the π-bond orders are important.     

Substituent chemical shifts of the organotin moiety in compounds of the type RSnMenCl3 − n (n = 0 to 3; R = n-alkyl)

The ¹³C and ¹¹⁹Sn NMR spectra of 33 organotin compounds of the type RSnMe_nCl_{3 ? n} and related types are discussed. The substituent effects of the groups SnMe₃, SnMe₂Cl, SnMeCl₂ and SnCl₃ (and of some related groups) on the carbon chemical shifts in the alkyl group R have been determined; the SnMe₃ group causes a small upfield shift of the carbon attached to it, while the other groups cause downfield shifts. The shifts show a monotonic change on replacing methyl groups in Me₃Sn by chlorine atoms. The effects on carbons further removed from the tin atom are discussed. Variation in R causes little change in ⁿJ(Sn? C) or δ(¹¹⁹Sn).