13C‐NMR data of daphnane diterpenoids

Daphnane diterpenoids are mainly distributed in Thymelaeaceae and Euphorbiaceae and have various bioactivities. About 100 daphnane diterpenoids have been isolated from natural plants. In this review, we systematically summarize the ¹³C‐NMR data of daphnane diterpenoids isolated from natural plants over the past several decades and briefly discussed their biological activities and basic structural–activity relationship. Copyright © 2013 John Wiley & Sons, Ltd.     

13C isotope effects on 1H chemical shifts: NMR spectral analysis of 13C‐labelled D‐glucose and some 13C‐labelled amino acids

The one‐ and two‐bond ¹³C isotope shifts, typically ?1.5 to ?2.5 ppb and ?0.7 ppb respectively, in non‐cyclic aliphatic systems and up to ?4.4 ppb and ?1.0 ppb in glucose cause effects that need to be taken into account in the adaptive NMR spectral library‐based quantification of the isotopomer mixtures. In this work, NMR spectral analyses of some ¹³C‐labelled amino acids, D ‐glucose and other small compounds were performed in order to obtain rules for prediction of the ¹³C isotope effects on ¹H chemical shifts. It is proposed that using the additivity rules, the isotope effects can be predicted with a sufficient accuracy for amino acid isotopomer applications. For glucose the effects were found strongly non‐additive. The complete spectral analysis of fully ¹³C‐labelled D ‐glucose made it also possible to assign the exocyclic proton signals of the glucose. Copyright © 2009 John Wiley & Sons, Ltd.     

Deuterium‐induced isotope effects on the 13C chemical shifts of α‐d‐glucose pentaacetate

1,2,3,4,6‐Penta‐O‐acetyl‐α‐d ‐glucopyranose and the corresponding [1‐²H], [2‐²H], [3‐²H], [4‐²H], [5‐²H], and [6,6‐²H₂]‐labeled compounds were prepared for measuring deuterium/hydrogen‐induced effects on ¹³C chemical shift ⁿΔ (DHIECS) values. A conformational analysis of the nondeuterated compound was achieved using density functional theory (DFT) molecular models that allowed calculation of several structural properties as well as Boltzmann‐averaged ¹³C NMR chemical shifts by using the gauge‐including atomic orbital method. It was found that the DFT‐calculated C–H bond lengths correlate with ¹Δ DHIECS. Copyright © 2013 John Wiley & Sons, Ltd.     

Study of phenothiazine and N‐methyl phenothiazine by infrared,raman, 1H‐, and 13C‐NMR spectroscopies

A complete vibrational analysis of the Fourier transform (FT) infrared (IR) and FT‐Raman spectra of both molecules was carried out using quantum chemical calculations. The structure of phenothiazine (PTZ) and N‐methylphenothiazine (N‐MePTZ) were studied by semiempirical, and ab initio methods. Different basis sets and two new procedures for scaling the frequencies of the ring modes were used. Vibrational data of the methyl group in N‐MePTZ were interpreted in terms of the different molecular conformations in the solid state. The ¹H‐ and ¹³C–nuclear magnetic resonance (NMR) data were interpreted in terms of the electron densities on the atoms and the stacking solute–solute association in dimethyl sulfoxide solution. Chemical shifts were related to the Merz‐Kollman atomic charges. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Comparison of the substituent effects on the 13C NMR with the 1H NMR chemical shifts of CHN in substituted benzylideneanilines

Fifty‐two samples of substituted benzylideneanilines XPhCH?NPhYs (XBAYs) were synthesized, and their NMR spectra were determined in this paper. Together with the NMR data of other 77 samples of XBAYs quoted from literatures, the ¹H NMR chemical shifts (δ_H(CH?N)) and ¹³C NMR chemical shifts (δ_C(CH?N)) of the CH?N bridging group were investigated for total of 129 samples of XBAYs. The result shows that the δ_H(CH?N) and δ_C(CH?N) have no distinctive linear relationship, which is contrary to the theoretical thought that declared the δ_H(CH?N) values would increase as the δ_C(CH?N) values increase. With the in‐depth analysis, we found that the effects of σ_F and σ_R of X/Y group on the δ_H(CH?N) and the δ_C(CH?N) are opposite; the effects of the substituent specific cross‐interaction effect between X and Y (Δσ²) on the δ_H(CH?N) and the δ_C(CH?N) are different; the contributions of parameters in the regression equations of the δ_H(CH?N) and the δ_C(CH?N) [Eqns 4 and 7), respectively] also have an obvious difference. Copyright © 2015 John Wiley & Sons, Ltd.     

Hydroacridines: Part 30. 1H and 13C NMR spectra of 9‐substituted 1,2,3,4,5,6,7,8‐octahydroacridines and of their N‐oxides

The ¹H and ¹³C NMR chemical shifts of 1,2,3,4,5,6,7,8‐octahydroacridine, 12 of its 9‐substituted derivatives, and of the corresponding N‐oxides were determined, assigned, and discussed in terms of 9‐substituent effects and effects of N‐oxidation. A good linear correlation was found between the ¹³C chemical shifts of the aromatic carbons in octahydroacridines and those of respective carbons in the corresponding N‐oxides. Copyright © 2009 John Wiley & Sons, Ltd.     

1H‐ und 13C‐NMR‐Spektroskopie

The present state of the routine 1D ¹H‐ and ¹³C‐NMR spectroscopy is reported. After a short introduction into the basic theory the current spectrometer and software systems are discussed. Using an example from natural product chemistry the procedures during the analysis of the NMR spectra are explained.     

1,2‐, 1,7‐ and 1,12‐Dicarba‐closo‐dodecaborane(12) Derivatives Revisited by 13C NMR Spectroscopy and DFT Calculations. First Observation of Isotope‐Induced Chemical Shifts 1Δ10/11B(13C), and the Signs and Magnitudes of Coupling Constants 1J(13C,13C) and 1J(13C,11B)

The origin of broadening of ¹³C(carborane) NMR signals of 1,2‐, 1,7‐ and 1,12‐dicarba‐closo‐dodecaboranes(12) and several diphenylsilyl derivatives has been examined in detail and could be traced only partially to unresolved ¹³C–¹¹B spin‐spin coupling. Other contributions to the line widths arise from ¹³C–¹H dipole‐dipole interactions and, in particular, from isotope‐induced chemical shifts ¹Δ^10/11B(¹³C), observed here for carboranes for the first time. In the case of 1‐diphenylsilyl‐1,2‐dicarba‐closo‐dodecaborane(12), the coupling constant ¹J(¹³C,¹³C) = 9.3 Hz was measured in natural abundance of ¹³C. The small value of this coupling constant and its negative sign is predicted by calculations based on optimised structures [B3LYP/6‐311+G(d,p) level of theory] of the parent carboranes and 1‐silyl‐1,2‐dicarba‐closo‐dodecaborane(12) as a model compound [calcd. ¹J(¹³C,¹³C) = –10.5 Hz]. Calculated coupling constants ¹J(¹³C,¹¹B) are small (<7 Hz), in contrast to published assumptions, and of either sign, whereas ¹J(¹¹B,¹¹B) are all positive and range up to 15 Hz.     

Substituent Effects on 13C NMR and 1H NMR Chemical Shifts of CH=N in Multi-substituted Benzylideneanilines

Fifty-three samples of multi-substituted benzylideneanilines XArCH=NArYs (abbreviated XBAYs) were synthesized and their NMR spectra were determined. An extensional study of substituent effects on the ¹H NMR chemical shifts (^δH(CH=N)) and ¹³C NMR chemical shifts (^δC(CH=N)) of the CH=N bridging group from di-substituted to multi-substituted XBAYs was made based on a total of 182 samples of XBAYs, together with the NMR data of other 129 samples of di-substituted XBAYs quoted from literatures. The results show that the substituent specific cross-interaction effect parameter \begin{document} $\left(\Delta\left(\displaystyle\sum\sigma\right)^2\right)$ \end{document} plays an important role in quantifying the ^δC(CH=N) values of XBAYs, but it is negligible for quantifying the ^δH(CH=N) values; the other substituent parameters also present different influences on the ^δC(CH=N) and ^δH(CH=N). On the whole, the contributions of X and Y to the ^δC(CH=N) of XBAYs are balanced, but the ^δH(CH=N) values of XBAYs mainly rely on the contributions of X.     

Tautomerism and 1H and 13C NMR assignment of methyl derivatives of 9-hydroxyphenalenone

9-Hydroxyphenalenone is a planar multicyclic beta-keto-enol that demonstrates C2V symmetry on the NMR timescale. Off-axis substitution breaks the molecular symmetry and results in tautomers. 1H and 13C NMR assignments were made for 9-hydroxyphenalenone and three methyl derivatives, and the solution-phase tautomers were determined.     

Disentangling Complex Mixtures of Compounds with Near‐Identical 1H and 13C NMR Spectra using Pure Shift NMR Spectroscopy

The thorough analysis of highly complex NMR spectra using pure shift NMR experiments is described. The enhanced spectral resolution obtained from modern 2D HOBS experiments incorporating spectral aliasing in the ¹³C indirect dimension enables the distinction of similar compounds exhibiting near‐identical ¹H and ¹³C NMR spectra. It is shown that a complete set of extremely small Δδ(¹H) and Δδ(¹³C) values, even below the natural line width (1 and 5 ppb, respectively), can be simultaneously determined and assigned.     

Characterization of 2‐aryl‐1,3,4‐oxadiazoles by 15N and 13C NMR spectroscopy

¹⁵N NMR chemical shifts of 2‐aryl‐1,3,4‐oxadiazoles were assigned on the basis of the ¹H–¹⁵N HMBC experiment. Chemical shifts of the nitrogen and carbon atoms in the oxadiazole ring correlate with the Hammett σ‐constants of substituents in the aryl ring (r² ≥ 0.966 for N atoms). ¹⁵N NMR data are a suitable and sensitive means for characterizing long‐range electronic substituent effects. Additionally, ¹³C NMR data for these compounds are presented. Copyright © 2003 John Wiley & Sons, Ltd.     

1H, 13C and 15N NMR spectral analysis of substituted 1,2,3,4‐tetrahydro‐pyrido[1,2‐a]pyrimidines

The NMR spectroscopic data of a series of thirty‐four 3‐acylpyrido[1,2‐a]pyrimidinium salts are analyzed, which were prepared as either perchlorates or chlorides. Methyl group substituted 3‐aroyltetrahydropyrido[1,2‐a]pyrimidines with the methyl substituent in positions 6, 8 and 9 as well as both in positions 6 and 8 were investigated bearing various aroyl substituents. Unequivocal assignment of all resonances was achieved via two‐dimensional ¹H,¹H‐COSY measurements, ¹H,¹³C and ¹H,¹⁵N HSQC as well as HMBC experiments, and important diagnostic CH and NH couplings in the heteroaromatic ring system are evaluated. The influence of the methyl substituents was analyzed on the proton, carbon and nitrogen shifts. A significant effect of the counter ion on some chemical shifts of the nuclei under discussion of the pyridopyrimidines is found, allowing the indirect detection of the anion, which is confirmed by direct measurement of the ³⁵Cl nucleus of the perchlorates. Copyright © 2013 John Wiley & Sons, Ltd.     

Complete assignment of 1H and 13C NMR spectra of α‐phenylsulfinyl‐N‐methoxy‐ N‐methylpropionamide and some p‐substituted derivatives

The complete assignment of the ¹H and ¹³C NMR spectra of the diastereomeric pairs of some α‐arylsulfinyl‐substituted N‐methoxy‐N‐methylpropionamides with the substituents methoxy, methyl, chloro, nitro is reported. Copyright © 2008 John Wiley & Sons, Ltd.     

1H and 13C NMR study of 2‐hydroxyglutaric acid and its lactone

Determination of the level and absolute configuration of 2‐hydroxyglutaric acid in a patient's urine is a method of diagnosing two metabolic diseases. Such a determination can be done with the aid of NMR spectroscopic methods. In this paper the careful interpretation of ¹H and ¹³C NMR spectra of this metabolite and its lactone measured under conditions used in biomedical assays is reported. The ¹H chemical shifts and spin–spin coupling constants were derived using the total lineshape analysis method. Copyright © 2002 John Wiley & Sons, Ltd.     

NMR Backbone Assignment of Large Proteins by Using 13Cα‐Only Triple‐Resonance Experiments

Nuclear magnetic resonance (NMR) is a powerful tool to interrogate protein structure and dynamics residue by residue. However, the prerequisite chemical‐shift assignment remains a bottleneck for large proteins due to the fast relaxation and the frequency degeneracy of the ¹³C_α nuclei. Herein, we present a covariance NMR strategy to assign the backbone chemical shifts by using only HN(CO)CA and HNCA spectra that has a high sensitivity even for large proteins. By using the peak linear correlation coefficient (LCC), which is a sensitive probe even for tiny chemical‐shift displacements, we correctly identify the fidelity of approximately 92 % cross‐peaks in the covariance spectrum, which is thus a significant improvement on the approach developed by Snyder and Brüschweiler (66 %) and the use of spectral derivatives (50 %). Thus, we calculate the 4D covariance spectrum from HN(CO)CA and HNCA experiments, in which cross‐peaks with LCCs above a universal threshold are considered as true correlations. This 4D covariance spectrum enables the sequential assignment of a 42 kDa maltose binding protein (MBP), in which about 95 % residues are successfully assigned with a high accuracy of 98 %. Our LCC approach, therefore, paves the way for a residue‐by‐residue study of the backbone structure and dynamics of large proteins.     

1H, 13C and 15N NMR chemical shifts of substituted pyrazolo[1,5‐a]pyrimidines

¹H, ¹³C and ¹⁵N NMR chemical shifts of 10 substituted pyrazolo[1,5‐a]pyrimidines were assigned based on DQF ¹H, ¹H COSY, PFG ¹H, ¹³C HMQC and PFG ¹H,X (X = ¹³C and ¹⁵N) HMBC experiments and on literature data. Copyright © 2002 John Wiley & Sons, Ltd.     

1H, 13C and 15N NMR investigation of a new,condensed hexahydro‐1,3,5‐triazine

Treatment of 2‐acetyl‐2‐methylcyclopentanone with hydrazine hydrate yielded a new condensed hexahydro‐1,3,5‐triazine (3b), which is the first example of the ketimine‐type trimers. A complete ¹H, ¹³C and ¹⁵N NMR assignment of the compound was achieved. Copyright © 2003 John Wiley & Sons, Ltd.     

3‐Methylflavones characterization revisited: complete assignment of 1H and 13C NMR data

Ten 3‐methylflavone derivatives were studied. Previously reported NMR data of some derivatives were corrected and/or completed, including the complete assignment of the two known natural derivatives. The complete ¹H and ¹³C NMR assignments were achieved by combination of one‐dimensional and two‐dimensional NMR experiments. Copyright © 2013 John Wiley & Sons, Ltd.