Analysis of 1H and 13C{1H} NMR Spectral Parameters and Geometries of Three Isomeric Diphenylbicyclo[2.2.1]Hept-5-Ene-2,3-Dicarboxylic Anhydrides

Diels-Alder adducts of 1,4-diphenyl-1,3-cyclopentadiene and maleic anhydride were investigated by recording the ¹H and ¹³C{¹H} NMR spectra of three isomeric diphenylbicyclo[2.2.1]hept-5-ene endo and exo 2,3-dianhydrides. the spectra were recorded in CD₂Cl₂ and analysed completely. the effect of the endo and exo configuration of the anhydride ring on the chemical shifts of the bridgehead phenyl protons is discussed. the ortho protons of the exo isomers resonate at higher field than those of the endo isomer, and the resonance pattern of the aromatic protons is narrower in the exo than the endo anhydride. the aromatic regions of the spectra are compared with the same regions of the ¹H NMR spectra of the earlier investigated addition products of 1,4-di-p-tolyl-1,3-cyclopentadiene and 1-phenyl-4-p-tolyl-1,3-cyclopentadiene with maleic anhydride. Chemical shifts of the bridge protons are explained on the basis of X-ray data of the compounds and MacroModel calculations on the minimum energy conformations.     

Proton Dynamics in Letovicite, (NH4)3H(SO4)2: A H and N NMR Spectroscopic Study

The improper ferroelastic phase letovicite (NH₄)₃H(SO₄)₂ has been studied by ¹H MAS NMR as well as by static ¹⁴N NMR experiments in the temperature range of 296–425 K. The ¹H MAS NMR resonance from ammonium protons can be well distinguished from that of acidic protons. A third resonance appears just below the phase transition temperature which is due to the acidic protons in the paraelastic phase. The lowering of the second moment M₂ for the ammonium protons takes place in the same temperature range as the formation of domain boundaries, while the signals of the acidic protons suffer a line narrowing in the area of T_c. The static ¹⁴N NMR spectra confirm the temperature of the motional changes of the ammonium tetrahedra. Two-dimensional ¹H NOESY spectra indicate a chemical exchange between ammonium protons and the acidic protons of the paraphase.     

Structural Assignment of Isomeric S‐ and S,N‐1‐Alkoxycarbonylalkylated 6‐Amino‐2‐thiouracil Derivatives by Means of 1H and 13C NMR Spectroscopy

Abstract

The structures of new isomeric 2‐alkoxycarbonylalkylthio‐ and 2‐alkoxy‐ carbonylalkylthio‐1‐alkoxycarbonylalkyl‐6‐aminouracils (1–21) have been established on the basis of the ¹H NMR and ¹³C NMR spectroscopic data. The ¹H NMR and ¹³C NMR spectra of 1–21 have been fully assigned by a combination of two‐dimensional experiments [heteronuclear multiple quantum coherence (HMQC) and heteronuclear multiple bond correlation (HMBC)]. The ¹³C NMR spectra have been shown to be able to differentiate between isomers.     

Assignments of 1H and 13C NMR Spectral Data for Benzoylecgonine,a Cocaine Metabolite

The complete assignment of the ¹H and ¹³C NMR spectra of benzoylecgonine, a cocaine metabolite, was performed, with the aid of some 2D experiments such as gCOSY and gHSQC.     

NMR Studies of Hindered Rotation and Magnetic Anisotropy: The Diels–Alder Adducts of Phencyclone with N‐Phenylmaleimide and N‐(2‐Trifluoromethylphenyl)maleimide. Ab Initio Calculations for Optimized Structures

Abstract

N‐Phenylmaleimide, 2, and N‐(2‐trifluoromethylphenyl)maleimide, 3, were separately added to phencyclone, 1, to yield the corresponding phencyclone Diels–Alder adducts, 4 and 5. The resulting adducts (and some precursors) have been characterized by one‐ and two‐dimensional ¹H and ¹³C NMR at 300 and 75 MHz, and by ¹⁹F NMR at 282 MHz, at ambient temperatures. The NMR data are consistent, for both adducts, with: (a) hindered rotation of the bridgehead unsubstituted phenyl groups about the C(sp²)–C(sp³) bonds, based on slow exchange limit (SEL) spectra and (b) endo adduct configuration based on magnetic anisotropic effects in the ¹H NMR. The NMR spectra of the phencyclone adduct, 4, of N‐phenylmaleimide, indicate free rotation on the NMR timescales (fast exchange limit, FEL spectra) about the N‐phenyl bond. The spectra for the adduct, 5, of N‐(2‐trifluoromethylphenyl)maleimide are interpreted as consistent with SEL regimes, for the N‐aryl rotations, with a single rotamer present in which the trifluoromethyl group is directed “out of” the adduct cavity, and away from the phenanthrenoid moiety. This conclusion is based, in part, on NMR data suggesting the apparent slow N‐aryl bond rotation in a pair of atropisomers corresponding to the acetic acid addition products from the N‐(2‐trifluoromethylphenyl)maleimide. Evidence of magnetic anisotropic effects due to the phenanthrenoid moiety and proximal carbonyls is discussed. ¹H, ¹³C, and ¹⁹F assignments are presented and interpreted. Molecular modeling calculations at the Hartree–Fock level, 6‐31G* basis set, were performed to provide geometry optimizations for energy‐minimized structures of selected compounds.     

NMR Studies of Hindered Rotation. The Diels-Alder Adduct of 4-Methyl-1, 2, 4-triazoline-3, 5-dione with Phencyclone: Restricted Motion of Unsubstituted Bridgehead Phenyls.

4-Methyl-1, 2, 4-triazoline-3, 5-dione was produced by lead tetraacetate oxidation of 4-methylurazole and allowed to react with phencyclone, 1-The resulting Diels-Alder adduct, 2, has been characterized by one-and two-dimensional ¹H and ¹³C NMR at 300 and 75 MHz, respectively, at ambient temperatures in different solvents. The NMR data are consistent with hindered rotation of the bridgehead unsubstituted phenyl groups about the C(sp²)-C(sp³) bonds, based on numbers of absorption signals in the ¹H and ¹³C NMR aryl region, together with magnetic anisotropic effects in the ¹H spectrum. The spectral simplicity suggests further that stereochemistry at the ring junction nitrogens involves only a single isomer or very rapidly interconverting “exo”/“endo” isomers (if the ring junction nitrogens are pyramidalized).     

13C NMR Chemical Shifts of Heterocycles: Empirical Substituent Effects in 5-Halomethylisoxazoles

Evaluation by empirically derived equations for the Substituent effect (α, β, γ, δ) on the ¹³C NMR chemical shifts for C-3, C-4. C-5 and halomethyl-substituent carbon (C-6) in isoxazoles 1-5 [where C-3 substituent (R¹) = H, alkyl or phenyl, C-4 Substituent (R²) = H, alkyl, and C-5 substituent (R³) = di-or trihalomethyl, methyl and H], taking as reference the compound la, is reported. From the calculated values for the α, β, γ, δ effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1–5. The ¹³ C chemical shifts of the C-3, C-4, C-5, C-6 of these compounds, can be estimated with good precision: 94% of the calculated chemical shifts are found to be within ±1.0ppm, and 100% are found to be within ±1.5ppm.     

NMR Studies of Hindered Rotation. The Diels-Alder Adduct of Phencyclone with N-n-Propylmaleimide: Restricted Motion of Bridgehead Phenyls

The Diels-Alder adduct of phencyclone and N-n-propylmaleimide has been studied in CDCl₃ solution at ambient temperatures by one-and two-dimensional ¹H NMR (300 MHz) and ¹³C NMR (75 MHz) techniques. Clear evidence is presented from slow exchange limit (SEL) spectra for hindered rotation of the bridgehead phenyls in the adduct. Full ¹H spectral assignments have been made via selective homonuclear decoupling and high resolution COSY experiments. The number of signals in the aryl region of ¹³C NMR spectra also indicated slow rotation about the C(sp²)-C(sp³) bond to the unsubstantiated bridgehead phenyls. Striking evidence of magnetic anisotropic effects, seen from ¹H NMR, permits stereochemical assignment of the adduct as endo.     

Na and H NMR Microimaging of Intact Plants

²³Na NMR microimaging is described to map, for the first time, the sodium distribution in living plants. As an example, the response of 6-day-old seedlings of Ricinus communis to exposure to sodium chloride concentrations from 5 to 300 mM was observed in vivo using ²³Na as well as ¹H NMR microimaging. Experiments were performed at 11.75 T with a double resonant ²³Na–¹H probehead. The probehead was homebuilt and equipped with a climate chamber. T₁ and T₂ of ²³Na were measured in the cross section of the hypocotyl. Within 85 min ²³Na images with an in-plane resolution of 156 × 156 μm were acquired. With this spatial information, the different types of tissue in the hypocotyl can be discerned. The measurement time appears to be short compared to the time scale of sodium uptake and accumulation in the plant so that the kinetics of salt stress can be followed. In conclusion, ²³Na NMR microimaging promises great potential for physiological studies of the consequences of salt stress on the macroscopic level and thus may become a unique tool for characterizing plants with respect to salt tolerance and salt sensitivity.     

NMR Studies of Hindered Rotation. The Diels-Alder Adduct of N-n-Butylmaleimide With Phencyclone: Restricted Motion of Bridgehead Phenyls

The Diels-Alder adduct of phencyclone and N-n-butylmaleimide has been prepared, and NMR studies have been carried out in CDCl₃ solution at ambient temperatures by one-and two-dimensional ¹H NMR (300 MHz) and ¹³C NMR (75 MHz) techniques. The resulting spectra appear to be consistent with slow rotation about the hindered C(sp²)-C(sp³) bonds to the bridgehead unsubstituted phenyls, i.e., slow exchange limit (SEL) spectra. Full rigorous ¹H spectral assignments have been made via high-resolution COSY experiments. The number of signals in the ¹³C NMR aryl region were also consistent with hindered phenyl rotations; preliminary ¹³C assignments are given. Striking evidence for magnetic anisotropic effects due to the phenanthrene moiety, bridging ketone carbonyl, and bridgehead phenyls are discussed, supporting endo stereochemical assignment of the adduct.     

1H and 13C NMR Spectral Study of Some 2r-Aryl-6c-phenylthian-4-ones,Their 1-Oxides and 1,1-Dioxides

ABSTRACT

Four 2r-aryl-6c-phenylthian-4-ones 1b?1e and their 1-oxides 2b?2e and 1,1-dioxides 3b?3e have been newly synthesized. ¹H and ¹³C NMR spectra have been recorded for all these compounds and 2r,6c-diphenylthian-4-one 1-oxide 2a. ¹³C NMR spectrum has been recorded for the sulfone 3a of 1a. For selected compounds ¹H-¹H COSY, HSQC, HMBC, and NOESY spectra have been recorded. The vicinal proton–proton coupling constants suggest that in all these compounds, the heterocyclic ring adopts chair conformation with equatorial orientations of the aryl and phenyl groups. Proton and carbon chemical shifts suggest that in the sulfoxides, the S=O bond is axial and enhances the J _aa value by some special effect. The S = O bond causes a significant upfield shift even on carbons without hydrogens. Significant solvent shifts also were observed.     

Detection and Characterization of Boric Acid and Borate Ion Binding to Cytochrome c Using Multiple Quantum Filtered NMR

The application of multiple quantum filtered (MQF) NMR to the identification and characterization of the binding of ligands containing quadrupolar nuclei to proteins is demonstrated. Using relaxation times measured by MQF NMR multiple binding of boric acid and borate ion to ferri and ferrocytochrome c was detected. Borate ion was found to have two different binding sites. One of them was in slow exchange, k_diss = 20 ± 3 s⁻¹ at 5°C and D₂O solution, in agreement with previous findings by ¹H NMR (G. Taler et al., 1998, Inorg. Chim. Acta 273, 388–392). The triple quantum relaxation of the borate in this site was found to be governed by dipolar interaction corresponding to an average B–H distance of 2.06 ± 0.07 Å. Other, fast exchanging sites for borate and boric acid could be detected only by MQF NMR. The binding equilibrium constants at these sites at pH 9.7 were found to be 1800 ± 200 M⁻¹ and 2.6 ± 1.5 M⁻¹ for the borate ion and boric acid, respectively. Thus, detection of binding by MQF NMR proved to be sensitive to fast exchanging ligands as well as to very weak binding that could not be detected using conventional methods.     

Azetidin‐2‐one Versus Chroman‐2‐one: Application of 1H‐13C COSY NMR and Mass Spectroscopy in Structure Elucidation–Class of Compounds

Azetidin‐2‐ones, commonly known as β‐lactams, constitute a biologically important class of compound. Treatment of azetidin‐2‐ones with alkali is known to form diverse types of compounds depending on the stability of the ring. In many cases, the ring is retained in the product at the cost of transformation of substituents. Spectroscopy is the most important tool to characterize the organic compounds. However, in some cases the structures of the products are so closely related that simple IR, ¹H NMR, and ¹³C NMR spectra do not lead to unambiguous structure elucidation. This article reports a novel application of ¹H‐¹³C COSY NMR and mass spectroscopy in determining unequivocally an azetidin‐2‐one ring structure instead of a chroman‐2‐one ring structure for the product obtained by treatment of 1‐benzhydryl‐3,3‐bis(4‐methylphenyl)‐4‐[2‐(o‐dip‐tolylacyl)hydroxyphenyl]‐2‐azetidinone with ethanolic sodium hydroxide at room temperature.     

Assignment of the 1H and 13C Spectra of 5-Methylthio-4H-1-(p-R1-phenyl)-3a-(p-R2-phenyl)-3a,4-dihydro (1,2,4) oxadiazolo(4,5-a), 1,5-benzodiazepines using 2D NMR Spectroscopy.

The ¹H NMR spectra of the title benzodiazepines derivatives is highly congested because all the protons are in aromatic enviroment so many proton signals remain overlap even 300 MHz or higher fields. With this in mind, the assignment of the ¹H and ¹³C spectra of these compounds obtained using COSY, NOESY, HMQC and HMBC experiments is reported.     

Determination of the Stereochemistry of Substituted 5-Methylenehydantoins and Thiohydantoins by 13C NMR and Homonuclear NOE Experiments

Basically the aim of this work is to define the accurate configuration of the exocyclic double bond of substituted 5-methylenehydantoins and thiohydantoins which have been conceived as potential Aldose Reductase inhibitors. A previsional survey based upon the chemical shifts analysis from ¹H and decoupled ¹³C NMR spectra discloses, for a part of the family of compounds, the assignment of the Zconfiguration for unsubstituted (2,3) and N-3 substituted (6,7,9) derivatives, and the E-configuration for the N-1 substituted (8,11) ones. The qualitative study with Homonuclear NOE (8,11) and the coupling constant measuring ^{3 J}C4-C=C-H6 from coupled ¹³C NMR (1–11), lead to the assignment of the accurate configuration of the whole family's compounds in agreement with the previsional study.     

C-13 and H-1 NMR Assignments of the Chamigrenes Prepacifenol and Dehydroxyprepacifenol Epoxioes

A complete assignment of the signals in the ¹H and ¹³C NMR spectra and the stereostructural analysis of the compounds prepacifenol epoxide and the new dehydroxyprepacifenol epoxide are presented. These compounds were extracted from the marine mollusc Aplysia dactylomela and represent the first occurrence of chamigrenes found in Brazilian waters. The NMR analyses are supported by NOE difference and COSY experiments and also by gradient selected HMBC, HSQC-TOCSY and HSQC-DE. ¹H spectra simulations were done for the final fitting of the chemical shifts and coupling constants.     

Structural Assignment of Stilbenethiols and Chalconethiols and Differentiation of Their Isomeric Derivatives by Means of 1H‐ and 13C‐NMR Spectroscopy

Abstract

The ¹H‐ and ¹³C‐NMR spectra of some substituted stilbenes and chalcones were assigned unambiguously on the basis of a combination of homo‐ (COSY) and heteronuclear (HETCOR) two‐dimensional methods, the chemical shifts, as well as spin‐coupling constants. The A_ik empirical parameters of the –O–C(S)–N(CH₃)₂, –S–C(O)–N(CH₃)₂, and –SH group were calculated to help predict the chemical shifts of substituted stilbenes, 4′‐nitrostilbenes, and chalcones. The ¹H‐ and ¹³C‐NMR spectra have been shown to be able to differentiate between the isomers of O‐stilbenyl (4, 5) and S‐stilbenyl N,N‐dimethylthiocarbamates (7, 8) as well as O‐chalconyl (6) and S‐chalconyl N,N‐dimethylthiocarbamates (9).     

Application of a New Program,H1MACH,for Prediction of Iridoid Skeletons

Abstract

A procedure is presented that utilizes ¹H NMR for prediction of the skeleton of iridoids. A new program was developed, named H1MACH, that presents a database with 800 data points from the ¹H NMR spectra of iridoids. This program was widely tested for the prediction of the skeleton of 40 compounds and compared with other programs in the expert system SISTEMAT. The results obtained show that H1MACH is very useful for the prediction of the skeleton of iridoids, especially for the iridane skeleton.     

Assignment of the 1H and 13C Spectra of 5-Methylthio-4H-1-(p-R1-phenyl)-3a-(p-R2-Phenyl)-3a, 4-dihydro (1,2,4) oxadiazolo(4,5-a), 1, 5-benzodiazepines Using 2D NMR Spectroscopy

The ¹H NMR spectra of the title benzodiazepines derivatives is highly congested because all the protons are in aromatic environment so many proton signals remain overlap even 300 MHz or higher fields. With this in mind, the assignment of the ¹H and ¹³C spectra of these compounds obtained using COSY, NOESY, HMQC and HMBC experiments is reported.     

Design and construction of a versatile dual volume heteronuclear double resonance microcoil NMR probe

Improved NMR detection of mass limited samples can be obtained by taking advantage of the mass sensitivity of microcoil NMR, while throughput issues can be addressed using multiple, parallel sample detection coils. We present the design and construction of a double resonance 300-MHz dual volume microcoil NMR probe with thermally etched 440-nL detection volumes and fused silica transfer lines for high-throughput stopped-flow or flow-through sample analysis. Two orthogonal solenoidal detection coils and the novel use of shielded inductors allowed the construction of a probe with negligible radio-frequency cross talk. The probe was resonated at ¹H–²D (upper coil) and ¹H–¹³C (lower coil) frequencies such that it could perform 1D and 2D experiments with active locking frequency. The coils exhibited line widths of 0.8–1.1 Hz with good mass sensitivity for both ¹H and ¹³C NMR detection. ¹³C-directly detected ²D HETCOR spectra of 5% v/v ¹³C labeled acetic acid were obtained in less than 5 min. Demonstration of the probe characteristics as well as applications of the versatile two-coil double resonance probe are discussed.