Carbon-13 NMR Spectra Research Articles

Isolating trans-Anethole from Anise Seeds and Elucidating Its Structure: A Project Utilizing One- and Two-Dimensional NMR Spectrometry

This three-week project involves isolating and purifying a natural product and determining its structure. trans-Anethole is isolated from anise seeds by steam distillation and liquid-liquid extraction. The crude product is analyzed by thin-layer chromatography and purified by flash chromatography. A variety of one- and two-dimensional NMR methods, along with infrared spectroscopy, are used to elucidate the structure. The one-dimensional NMR methods are proton homonuclear decoupling, Distortionless Enhancement by Polarization Transfer (DEPT), and Nuclear Overhauser Effect (NOE) difference spectroscopy. The two-dimensional NMR methods are proton-proton COrrelated SpectroscopY (COSY) and HETeronuclear CORrelated spectroscopy (HETCOR). Finally, the proton and carbon-13 NMR spectra are assigned.

Revised patterns of reactivity scheme. VII. Revised patterns scheme and its relationship to carbon-13 NMR spectra

The electron density on a carbon atom determines the 13C chemical shift observed in the NMR spectrum. In a vinyl monomer, the same electron density must contribute strongly to polar effects involved in the addition of a radical to that monomer and possibly in the addition (to a double bond) of a radical terminated by a unit derived from that monomer. It is shown that the expected correlation exists when the polar effects in polymerization reactions are represented by the parameters of the revised patterns scheme. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4336–4342, 2000

Nitrogen-containing apatite

Two commercial hydroxyapatites were treated in dry ammonia at temperatures between 800 and 1300°C for different times up to 30 h. Nitrogen was incorporated with a maximum content of 3·7 wt% in presence of graphite. X-ray diffraction studies show no important phase transformation by the incorporation of nitrogen up to 1200°C. Treatments at temperatures above 1200°C resulted in the formation of CaO or Ca(OH) 2. 31P NMR studies indicate no direct bonding of nitrogen and phosphorous. Infrared spectra show increasing intensities of four new bands at 3250, 2016, 1966 and 700 cm −1 with increasing nitrogen contents, while the OH-bands at 3570 and 630 cm −1 vanish. Taking into account results of the carbon content, XRD, NMR and IR spectra it is suggested that nitrogen enters into the structure as [CN 2] 2− ion, substituting [OH] − groups, and forming cyanamidapatite Ca 10(PO 4) 6(CN 2). ©

Synthesis and complete1Hand13C assignments of thiazolo[3,2-a]quinolinium derivatives

Several hitherto unknown thiazolo[3,2-a]quinolinium salts derivatives were prepared and characterized. Two-dimensional high field nmr methods were employed to make complete assignments of the proton and carbon nmr spectra for these compounds.

Redox active alkenyl-bridged bi- and trinuclear arene–Cr(CO) 3-complexes by Horner–Emmons–Wadsworth olefinations

Alkenyl-bridged arene–Cr(CO) 3-complexes 2 are readily synthesized in good yields by Horner–Emmons–Wadsworth (HEW) olefinations from Cr(CO) 3-complexed benzylphosphonates 1 and organometallic aldehydes. The resulting bi- and trinuclear homo- and heterometallic complexes display a strong electronic coupling between the metal fragments as shown by a strong correlation of the CO resonances in the carbon NMR spectra and the chromiumcarbonyl metal–ligand charge transfer (MLCT) bands in the UV/vis spectra. Furthermore, the electrochemistry of the oligonuclear complexes 2 was investigated by cyclic voltammetry.

Copolymerization of glycolide andε-caprolactone, 1. Analysis of the copolymer microstructure by means of1H and13C NMR spectroscopy

A detailed analysis of the structure of glycolide/e-caprolactone copolymers was performed using 13 C and 1 H NMR. All methylene and carbonyl carbons of glycolidyl and caproyl units in the 13 C NMR spectra were found to be sensitive to the microstructure. The 'H NMR spectra allow not only to determine the copolymer composition but also to analyze the chain microstructure. In the region of methylene protons of glycolide the resonance lines were ascribcd to a series of compositional sequences, including those formed as a result of transesterification reactions. Equations are presented which allow to calculate the average lengths of comonomer blocks, the extent of transesterification, and the degree of randomness of the chain from both carbon and proton NMR spectra.

A proton and carbon NMR spectroscopic study of 5‐substituted acenaphthenes

The proton and carbon NMR spectra of eight 5-substituted acenaphthenes were obtained. The 13C chemical shifts of C-6 and C-2a of these compounds were compared with those of carbons located at structurally similar positions in 1-substituted naphthalenes (viz. C-8 and C-4). The 13C chemical shifts of C-2a were also analysed using the dual substituent parameter (DSP) equation. The results revealed (i) diminished steric interactions between the 5-substituent and the adjacent peri-carbon (C-6) and (ii) an enhanced transmission of both polar and resonance effects to the carbon para (C-2a) to the variable substituent, X, in acenaphthenes relative to the corresponding carbons (C-4) in 1-substituted naphthalenes. The higher ρI and ρR values observed for C-2a of acenaphthenes suggest higher polarizability in this system than in naphthalenes. AM1 calculations of charge also showed enhanced substituent effects in the case of most of the substituents in the acenaphthene system. © 1998 John Wiley & Sons, Ltd.

The synthesis of novel polycyclic heterocyclic ring systems via photocyclization. 20. Benzo[h]thieno[3′,2′:4,5]thieno[2,3‐c]‐quinoline, benzo[f]thieno[3′,2′:4,5]thieno[2,3‐c]quinoline, benzo[f]thieno[3′,2′:4,5]thieno[2,3‐c]tetrazolo[1,5‐a]quinoline and benzo[f]thieno[3′,2′:4,5]thieno[2,3‐c][1,2,4]triazolo[4,3‐a]quinoline

AbstractFour previously unknown polycyclic heterocyclic ring systems, namely, benzo[h]thieno[3′,2′:4,5]‐thieno[2,3‐c]quinoline (6), benzo[h]thieno[3′,2′:4,5]thieno[2,3‐c]quinoline (11), benzo[f]thieno‐[3′,2′:4,5]thieno[2,3‐c]tetrazolo[1,5‐a]quinoline (12) and benzo[f]thieno[3′,2′:4,5]thieno[2,3‐c][1,2,4]‐triazolo[4,3‐a]quinoline (13), were synthesized via oxidative photocyclization. Unequivocal total assignments of the proton and carbon nmr spectra of 6 and 11 were made through the concerted usage of COSY, HMQC and HMBC two‐dimensional nmr spectroscopic methods.

13C NMR spectral assignment ofN-arylphthalisoimides

The complete assignment of the carbon NMR spectra for 14 N-arylphthalisoimides was achieved using the concerted application of one- and two-dimensional NMR techniques. The parameters previously reported in the literature were found to be wrong. ©1998 John Wiley & Sons, Ltd.

Broadband analytical decoupling in high-resolution NMR spectra

A data processing method, based on double integral calculations, to obtain decoupled high-resolution NMR spectra in the weak scalar coupling approximation is described. Data are recorded from conventional spin echo experiments using different values of the delay of the echo. The collected echoes are processed in the time domain in such a way that resonances appear as single lines at their chemical shift frequencies in the resulting spectrum. The method described is a two-step post-acquisition treatment. In the first step, broadband decoupling of the spectrum is achieved. The second processing step suppresses the modulation of the amplitude by the scalar coupling J. Finally the spectrum obtained may be presented in the pure absorption mode without J-modulation. This technique, designed by analytical decoupling, improves the signal-to-noise ratio and facilitates the interpretation of complicated spectra. Intensities are not modulated by scalar coupling and they can be employed for quantitative analysis. The method was applied to proton NMR spectra of diethyl ether and 6-vinyl-1,3-dioxane 1,3. It may be also applied to heteronuclear spin systems and an example of a broadband decoupled carbon-13 NMR spectrum of a mixture of diethyl ether and ethanol is given. © 1998 John Wiley & Sons, Ltd.

Meropenem Exists in Equilibrium with a Carbon Dioxide Adduct in Bicarbonate Solution

□ Evidence is provided for the existence of a second discrete chemical form of meropenem at clinically relevant concentrations prepared from the marketed formulation of the drug. Proton and carbon-13 NMR spectra in D2O, coupled with tandem mass spectroscopy (MS/MS) and cross polarization/magic angle spinning (CP-MAS) NMR experiments, allow structural assignment of the compound as a covalent carbon dioxide adduct of meropenem. This carbon dioxide adduct exists in equilibrium with the free drug in solution and can be observed in the solid state following lyophilization. The equilibrium constant of formation of the adduct (Keq=20±8M–1) was estimated in D2O at 25°C.

Carbon-13 NMR spectra of imidazole 1-oxides. Comparison with the parent imidazoles

The 13C chemical shifts and C–H coupling constants of a series of imidazole 1-oxides were compared with those of the parent imidazoles and imidazolium salts in order to show the influence of N-oxidation on these parameters. The 13C chemical shifts can be related to the electron density at the carbon atoms whereas long range C–H coupling constants can be related to the relative localization or delocalization of the π system in imidazoles, imidazolium salts and imidazole N-oxides. ©1998 John Wiley & Sons, Ltd.

Carbon-13 NMR spectra of imidazole 1-oxides. Comparison with the parent imidazoles

The 13C chemical shifts and C–H coupling constants of a series of imidazole 1-oxides were compared with those of the parent imidazoles and imidazolium salts in order to show the influence of N-oxidation on these parameters. The 13C chemical shifts can be related to the electron density at the carbon atoms whereas long range C–H coupling constants can be related to the relative localization or delocalization of the π system in imidazoles, imidazolium salts and imidazole N-oxides. ©1998 John Wiley & Sons, Ltd.

Complete assignment of1H and13C NMR spectra of ikarisoside A and epimedoside C

The complete assignment of the proton and carbon NMR spectra for ikarisoside A and epimedoside C from the aerial parts of Epimedium koreanum were achieved using the concerted application of one- and two-dimensional NMR techniques including COSY and HMBC spectroscopy. The parameters previously reported in the literature were found to be incorrect or incomplete. © 1997 John Wiley & Sons, Ltd.

Ferroelectric liquid crystals derived from isoleucine II. Orientational ordering by carbon-13 separated local field spectroscopy

The orientational ordering of a series of ferroelectric liquid crystals 4'-[(2S, 3S)-3-methyl- 2-halopentanoyloxy]-4-hexyloxybiphenyls (3M2XPHOB, X=F for fluorine, C for chlorine, B for bromine) and their racemates have been studied by two-dimensional carbon-13 separated local field spectroscopy combined with off-magic-angle spinning. All carbons are well-resolved in the carbon-13 NMR spectrum so that carbon-proton dipolar coupling constants for all carbons in the liquid crystal molecule can be determined, giving detailed segmental orienta- tional ordering information. (The order parameters of the biphenyl core segments and each carbon-proton bond in the aliphatic chains were measured as a function of temperature.) The results show that the substitution of different halogens on the chiral chain affects the carbon- proton bond orientational ordering of the entire chiral chain, while the orientational ordering of the rest of the liquid crystal molecule (core and achiral chain) remains unchanged. For the fluoro-substituted liquid crystals, carbon-fluorine dipolar couplings are also observed. At the SmA-to-SmC* transition, there is a discontinuous change in the magnitudes of all C-H bond order parameters. However, the aliphatic ordering relative to the core ordering is unchanged, suggesting that there is a negligible change in the mesogen conformation and the environment of the aliphatic chain at this transition, i.e. there is no evidence for substantial 'chiral interactions' in the SmC* phase.

Quantitative Description of the Facial Discrimination of Molecules Containing a Prochiral Group by NMR in a Chiral Liquid Crystal

The quantitative description of the facial discrimination in molecules containing a prochiral group oriented in a polypeptide liquid crystalline system is reported. From the analysis of proton, carbon-13, and deuterium NMR spectra of ethanol dissolved in an organic solution of poly-γ-(benzyl-l-glutamate) (PBLG), the full molecular order matrix and the principal axis system were determined. It is shown that five nonzero independent order parameters are necessary to describe correctly the molecular ordering of ethanol in this medium, which clearly demonstrates that in this chiral liquid crystal, the symmetry of the ordering in a prochiral molecule is broken. Due to the nonequivalence in terms of the dipolar couplings of the two enantiotopic protons of ethanol, it is possible to determine the sign and the magnitude of geminal scalar couplings between them. This new approach to obtain the geminal 2JHH constants is tested on a series of linear alcohols and compared to values derived from 2JHD of the same molecules by the isotopic substitution method.

Synthesis and Conformational Characteristics of Inherently Chiral Monoalkyl Ethers of p-tert-Butyldihomooxacalix[4]arene.

The synthesis of four inherently chiral monoalkyl ethers (methyl, ethyl, allyl, and benzyl), derived from p-tert-butyldihomooxacalix[4]arene, is described. Their conformational features were studied by variable temperature (1)H NMR spectroscopy in solvents with different polarity, such as chloroform (or CDCl(2)CDCl(2)), acetone, DMSO, and pyridine. Coalescence temperatures and DeltaG() were determined in CDCl(2)CDCl(2) and pyridine solutions. Monomethyl ether has a T(c) of 86 degrees C in CDCl(2)CDCl(2) and of -8 degrees C in pyridine, and the other derivatives are conformationally immobilized (DeltaG() >> 20 kcal mol(-1) in both solvents). The cone conformation, obtained for all monoethers, was confirmed by (13)C and NOESY spectra and also from a series of NOE 1D experiments. Complete assignment of both proton and carbon NMR spectra was achieved for the monomethyl ether by a combination of COSY, HMQC, and selective INEPT experiments, in chloroform at room temperature. Inherent chirality for all compounds was demonstrated by the addition of Pirkle's reagent to CDCl(3) solutions of monoethers derivatives, causing duplication of the NMR proton signals.

13C NMR Characterization of Guaiacyl, Guaiacyl/Syringyl and Syringyl Dehydrogenation Polymers

Summary Dehydrogenation polymers (DHPs) were prepared from coniferyl alcohol (CA), sinapyl alcohol (SA), and a mixture of coniferyl and sinapyl alcohol. The polymers were fully acetylated and their carbon NMR spectra were compared. Comparison of the 13C NMR spectra of the DHPs with those of authentic tri- and tetralignols facilitated the assignment of about 85% of the 117 reported signals. Most of the unassigned signals were those from syringyl units. Major differences between the DHP prepared from CA and a pine milled wood lignin were: a relative deficiency of s-O-4 linkages and a predominance of s-5, s-s, and CA end units in the DHP. In contrast, there was no significant quantity of SA end units in a DHP prepared from SA. A major conclusion of the study confirmed that DHPs prepared from CA are relatively poor models of natural lignins isolated from gymnosperms.

Determination of the sequence distribution and stereoregularity of ethyl ?-benzoyloxymethylacrylate?methyl methacrylate copolymers by means of proton and carbon-13 NMR

Proton and Carbon-13 NMR spectra of ethyl α-benzoyloxymethylacrylate (E)–methyl methacrylate (M) copolymers were analyzed in terms of sequence distribution and stereoregularity of monomer units. The copolymers were prepared by free radical polymerization in benzene at 50°C. The methoxy region of the M proton signal resonance was found to be sensitive to the copolymer composition for M-centred sequences. The carbon-13 NMR spectra of the EM copolymers, in particular the carbonyl signal resonances of carbomethoxy and carboethoxy groups, are discussed in terms of M- and E-centred configurational sequences. The experimental values were in excellent agreement with those calculated taken into account the terminal copolymerization model and Bernoullian distribution of stereoregularity with the statistical parameters determined from reactivity ratios rE = 0.32 and rM = 1.34 and the coisotacticity parameters σMM = 0.22, σEE = 0.70, and σME = σEM = σ = 0.30. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3483–3493, 1997

Determination of the sequence distribution and stereoregularity of ethyl α‐benzoyloxymethylacrylate—methyl methacrylate copolymers by means of proton and carbon‐13 NMR

Proton and Carbon-13 NMR spectra of ethyl α-benzoyloxymethylacrylate (E)–methyl methacrylate (M) copolymers were analyzed in terms of sequence distribution and stereoregularity of monomer units. The copolymers were prepared by free radical polymerization in benzene at 50°C. The methoxy region of the M proton signal resonance was found to be sensitive to the copolymer composition for M-centred sequences. The carbon-13 NMR spectra of the EM copolymers, in particular the carbonyl signal resonances of carbomethoxy and carboethoxy groups, are discussed in terms of M- and E-centred configurational sequences. The experimental values were in excellent agreement with those calculated taken into account the terminal copolymerization model and Bernoullian distribution of stereoregularity with the statistical parameters determined from reactivity ratios rE = 0.32 and rM = 1.34 and the coisotacticity parameters σMM = 0.22, σEE = 0.70, and σME = σEM = σ = 0.30. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3483–3493, 1997