Proton-proton coupling constants in the unsubstituted pyrylium cation

An iterative analysis of the PMR spectrum of the title compound was performed and the calculated values of spectral parameters, relative chemical shifts, proton-proton and direct carbon-proton couplings are compared with those of pyridine.     

二维NMR技术在有机结构分析中的应用

联合应用二维远程碳 -氢相关 (coloc)技术和二维碳 -氢相关(hxdept)技术 ,对三个含季碳较多的化合物进行了谱峰归属与结构指定。从而显示出多维NMR技术在有机结构分析中的重要作用。     

Reactive processing of polymers: Structural characterisation of products by H and C NMR spectroscopy for glycidyl methacrylate grafting onto EPR in the absence and presence of a reactive comonomer

Grafted GMA on EPR samples were prepared in a Thermo-Haake internal mixer by free radical melt grafting reactions in the absence (conventional system; EPR-g-GMA_CONV) and presence of the reactive comonomer divinyl benzene, DVB (EPR-g-GMA_DVB). The GMA-homopolymer (poly-GMA), a major side reaction product in the conventional system, was almost completely absent in the DVB-containing system, the latter also resulted in a much higher level of GMA grafting. A comprehensive microstructure analysis of the formed poly-GMA was performed based on one-dimensional ¹H and ¹³C NMR spectroscopy and the complete spectral assignments were supported by two-dimensional NMR techniques based on long range two and three bond order carbon-proton couplings from HMBC (Heteronuclear Multiple Bond Coherence) and that of one bond carbon-proton couplings from HSQC (Heteronuclear Single Quantum Coherence), as well as the use of Distortionless Enhancement by Polarization Transfer (DEPT) NMR spectroscopy. The unambiguous analysis of the stereochemical configuration of poly-GMA was further used to help understand the microstructures of the GMA-grafts obtained in the two different free radical melt grafting reactions, the conventional and comonomer-containing systems. In the grafted GMA, in the conventional system (EPR-g-GMA_CONV), the methylene protons of the GMA were found to be sensitive to tetrad configurational sequences and the results showed that 56% of the GMA sequence in the graft is in atactic configuration and 42% is in syndiotactic configuration whereas the poly-GMA was predominantly syndiotactic. The differences in the microstructures of the graft in the conventional EPR-g-GMA_CONV and the DVB-containing (EPR-g-GMA_DVB) systems is also reported     

INDO-SCPT calculations of the solvent dependence of some carbon-proton spin-spin coupling constants

Summary A theoretical study of the effects of non-specific solute-solvent interactions on the directly bonded carbon-proton couplings¹ J(C–H), in acetaldehyde, acetone and acrylonitrile is presented. The solvent induced changes in these couplings calculated by an INDO-SCPT procedure incorporating a modified solvaton model are in satisfactory agreement with experiment and show significant improvement over the INDO-FPT calculations using the Klopman-Germer solvaton model.

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INDO-SCPT-Rechnungen der Lösungsmittelabhängigkeit einiger C-H-Kopplungskonstanten

Zusammenfassung Es wird eine theoretische Studie zu den nichtspezifischen Lösungsmittelwechselwirkungen auf die Spin-Spin-Kopplungen direkt aneinander gebundener C- und H-Atome von Acetaldehyd, Aceton und Acrylnitril vorgestellt. Die vom Solvens induzierten Änderungen der Kopplungskonstanten werden von der INDO-SCPT-Methode unter Verwendung eines modifizierten Solvationsmodells zufriedenstellend wiedergegeben. Die Übereinstimmung mit den experimentellen Daten ist besser als INDO-FPT-Rechnungen mit dem Klopmann-Germer-Solvaton-Modell.

     

NMR and rotational angles in solution conformation of polypeptides

Professor San-Ichiro Mizushima and Professor Yonezo Morino's classical contributions provided unique means and firm basis for understanding of conformational states and internal rotation in polypeptide molecules. Now the NMR spectroscopy is the best choice to study molecular conformation, mechanism of action and structure-functional relationships of peptide and proteins in solution under conditions approaching those of their physiological environments. Crucial details of spatial structure and interactions of these molecules in solution are revealed by using proton-proton and carbon-proton vicinal coupling constants, proton nuclear Overhauser effect and spectral perturbation techniques. The results of NMR conformational analysis are presented for valinomycin “bracelet”, gramicidin A double helices, honey-bee neurotoxin apamin, scorpion insectotoxins and snake neurotoxins of long and short types.     

13C-NMR spectra and carbon-proton coupling constants of variously annulated furocoumarins

The ¹³C-nmr spectra of variously annulated methylfurocoumarins are reported. The assignments of chemical shifts for all the C resonances has been achieved by using carbon-proton coupling constants, relaxation efficiency considerations and shift effects caused by the introduction of methyl groups at various positions of the furocoumarin nucleus. Substituent effects on ¹³C chemical shifts and carbon-proton coupling constants are discussed.     

13C NMR spectra and carbon-proton coupling constants of various methylangelicins

The ¹³C-nmr spectra of various methyl derivatives of angelicin are reported. The assignment of chemical shifts for all the C atoms has been achieved by using carbon-proton coupling constants, nuclear Overhauser effect consideration and shift effects caused by the introduction of methyl groups on various positions of the angelicin nucleus. Substituent effects on ¹³C chemical shifts and carbon-proton coupling constants are discussed.     

13C n.m.r. spectra of 2-substituted pyrimidines

¹³C n.m.r. chemical shifts and carbon-proton coupling constants of 2-substituted pyrimidines are reported. The carbon chemical shifts are correlated with π-electron densities. Substituents which cause deshielding at the directly bound carbon (e.g. NH₂, OCH₃ and F) exert a more powerful effect in the benzene series than in the pyridine or pyrimidine series. The carbon-proton coupling constants do not correlate with the electronegativity of the substituents. Carbon-proton coupling constants and proton-proton coupling constants over the same number of bonds do not obey the Karabatsos relationship. The changes in the carbon-proton coupling constants in 2(1H)-pyrimidinone and 2(1H)-pyrimidinethione which accompany anion and cation formation are reported.     

Anti-plasmin inhibitor. VI. Structure of phlorofucofuroeckol A, a novel phlorotannin with both dibenzo-1,4-dioxin and dibenzofuran elements, from Ecklonia kurome Okamura

Phlorofucofuroeckol A (1), a novel phlorotannin with both dibenzo-1,4-dioxin and dibenzofuran elements, has been isolated from the brown alga Ecklonia kurome OKAMURA as a potent anti-plasmin inhibitor. Its structure has been elucidated to be 1,11-di(3,5-dihydroxyphenoxy)- benzofuro[3,2-a]dibenzo[b,e][1,4]dioxin-2,4,8,10,14-pentaol on the basis of the spectral data, in particular, by means of negative nuclear Overhauser effect (NOE) and long-range carbon-proton couplings (2JCH and 3JCH). Phlorofucofuroeckol A inhibited the action of alpha 2-macroglobulin (IC50 = 1.0 micrograms/ml) and alpha 2-plasmin inhibitor (IC50 = 0.3 micrograms/ml), the main plasmin inhibitors in plasma.     

NMR investigations of proline and its derivatives: Part 5. A semi-empirical calculation of the endo-exo equilibrium of the pyrrolidine ring and its pH-dependence

Exo-endo interconversion of the pyrrolidine ring of l-proline is studied, using the correlation of vicinal interproton couplings to the molecular geometry parameters via the sum of direct carbon-proton couplings.     

Structure and stereochemistry of a new cytotoxic polychlorinated sulfolipid from Adriatic shellfish

A detailed analysis of the causative toxins contained in the hepatopancreas of toxic mussels from the northern Adriatic sea has been carried out. Along with some DSP (diarrhetic shellfish poisoning) type toxins, such as okadaic acid, yessotoxin, and their derivatives, which are involved in a number of human intoxications throughout the world, we have now isolated a new cytotoxin, a polychlorinated sulfolipid 1, whose gross structure has been elucidated by spectral analysis, including various 2D NMR techniques. The relative stereochemistry of 1 was elucidated by successful application of the J-based configuration analysis developed for acyclic compounds using carbon-proton spin-coupling constants ((2,3)J(C,H)) and proton-proton spin-coupling constants ((3)J(H,H)); its absolute stereochemistry was established by the Mosher method. Compound 1 possesses in vitro cytotoxicity against WEHI 164 and RAW 264.7 cells.     

Application op vicinal carbon-proton coupling constants and molecular mechanics calculations in the conformational analysis of dioxolane rings

The conformation of the dioxolane ring of several bicyclic carbohydrate derivatives has been analyzed. The simuitaneous use of vicinal carbon-proton coupling constants and molecular mechanics calculations has demoonstrated to be useful in the conformational study of such a type of compounds.     

Carbon-13 NMR spectra of some 4- and 5-substituted pyrimidines

Carbon-13 NMR chemical shifts and carbon-proton coupling constants for nine 4-substituted and six 5-substituted pyrimidines are reported. The carbon chemical shifts are correlated with π-electron densities. Carbon-proton coupling constants fail to correlate with substituent electronegativity.     

Carbon-13 NMR spectroscopy of heterocyclic compounds—II : A 20 MHz study of chemical shifts and carbon-proton coupling constants for coumarin and some bromocoumarins

Complete assignments of chemical shifts and extensive assignments of carbon-proton coupling constants are presented for coumarin through a study also involving detailed measurements on 3-bromo-, 6-bromo-, 7-bromo-, 3,6-dibromo- and 3,6,8-tribromo-coumarin.     

Water-protein interactions in microcrystalline crh measured by 1H-13C solid-state NMR spectroscopy

Using solid-state NMR carbon-proton dipolar correlation spectroscopy, we observed hydrogen exchange on the millisecond time scale between water molecules and protein protons in a solid sample. These interactions are shown to be related to important structural features of the protein such as hydrogen-bonding or salt-bridge networks.     

Interpretation of the 13C NMR spectrum of physostigmine

The 25.1 MHz ¹³C nmr spectrum of physostigmine in deuteriochloroform has been reanalysed with the aid of high resolution proton coupled spectrum and selective proton irradiation experiments. In addition to unambiguous assignment the analysis yielded values for carbon-proton coupling constants.     

Temperature dependence of direct carbon-proton SSCC and stereoisomerism of substituted cyclic compounds

Conclusions It was shown from a study of the temperature dependence of direct carbon-proton SSCC for carbon atoms bound to a substituent in substituted cyclic compounds that it is possible to determine the preferential steric position of the substituents and the isomerism of the compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 818–822, April, 1986.     

Towards the automatic analysis of (1)H NMR spectra: Part 5. Confirmation of chemical structure with flow-NMR

A shift comparison procedure, which allows the use of flow spectra in automatic structure confirmation, is described. The effect of imperfect proton scaling at the analysis stage, loss of solute resonances under large solvent signals and the intermittent detection of labile protons are considered. The derivation of a suitable threshold acceptance criterion in the absence of explicit knowledge of spectral prediction reliability is also discussed.The methodology yielded approximately 10-15% incorrect structure confirmation, but the exact number depends on the reliability of spectral prediction and the number of incorrect but closely related structures postulated.     

Regioselective synthesis and structural elucidation of 1,4-disubstituted 1,2,3-triazole derivatives using 1D and 2D NMR spectral techniques

Regioselective synthesis of 2-[1-(2-oxo-2-phenylethyl)-1H-[1,2,3]triazol-4-ylmethoxy]-benzaldehyde derivatives was achieved by [3 + 2] cycloaddition reaction of 2-(prop)-2-ynyloxy-benzaldehyde derivatives with phenacyl azide. The regiochemistry and the spectral assignments of the synthesized triazole derivatives were studied using both 1D and 2D NMR spectral techniques in solution.     

1H and 13C-NMR data of hydroxyflavone derivatives

Many hydroxyflavone derivatives have been found in nature and shown to have many biological functions. Because their function is changed by the position and number of hydroxyl group, their structural identification is a fundamental and necessary step for understanding their functions. In the present study, the complete 1H and 13C NMR spectral assignments were presented for 6 hydroxyflavones, and NMR data of additional 14 hydroxyflavone derivatives were compared with those of the 6 hydroxyflavones. In addition, the partially incorrect NMR data of two of the dihydroxyflavones whose NMR data were previously reported were corrected.