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).     

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.     

Mono and bidimensional1H NMR and inverse detected13C NMR of the duplex d(CA)3·d(TG)3

The unambiguous assignment of the aromatic protons of the duplex d(CA)₃·d(TG)₃ was carried out with the aid of HMQC and HMBC inverse detected¹³C NMR experiments atT=278 K. The NOE connections of these protons with the imino protons of the complementary bases — established by 2D NOESY experiments — indicated that the duplex is characterized by a canonical Watson-Crick basepairing pattern. Monodimensional¹H NMR experiments, also carried out atT=278K, in the presence of varying amounts of NaCl and with water suppression by presaturation and by spin echo techniques, showed that the imino protons of the TA and CG pairs of the duplex exchange with water through a process of local base pair opening and with different exchange rates.     

低聚核苷酸d(GGTATACC)2的1H和13C NMR研究

通过综合分析2D ¹H NOE谱(混合时间100ms),¹³C-¹H异核多量子化学位移相关谱和¹H双量子滤波化学位移相关谱归属了低聚脱氧核糖核酸片断d(GGTATACC)₂ ¹H和¹³C的化学位移.该8聚核苷酸在溶液中为双螺旋B型结构,各碱基相对于糖环呈反式构象,糖环本身则均以C2'-endo构象为主.     

Isotope Effects by Comparing 1H‐ and 2D‐NMR Spectra of 9,9′‐Bisbicyclo[4.3.0]‐cyclonona‐2,4,7‐triene

Abstract

Inverse secondary kinetic isotope effects are determined for the dimerization of all‐cis‐cyclononatetraenyl radical, 1, to its corresponding dimer, all‐cis‐9,9′‐bicyclonona‐1,3,5,7‐tetraene, 2, (step 1, k _H/k _D=0.5), and cyclization of the latter to 9,9′‐bisbicyclo[4.3.0]cyclonona‐2,4,7‐triene, 3 (step 2, k _H/k _D=0.75). These results are obtained by comparison of ¹H‐ and ²D‐NMR spectra of 3 and employment of a simple statistical method for acquiring kinetic data. This new strategy appears superior to conventional methods in being fast, simple, and less expensive.     

1H and C-13 NMR Study of the Molecular Structure of New Di-(β-Keto) Schiff bases

New di-(β-keto) schiff bases were prepared. The molecular structure of those di-(β-keto) schiff bases was determined by ¹H and C-13 nmr spectroscopy.     

C-13 and H-1 NMR Study of Alkyl and Aryl-Substituted 1-(4′-Dimethylaminobenzylideneamino)pyridinium Perchlorates

C-13 and H-1 NMR spectra of some 1-(4′-dimethylaminobenzylideneamino)pyridinium perchlorates show that the angle of twist of the pyridine ring in unsubstituted, 1, and 2-alkyl substituted compounds 2–5 is comparable. However, it is considerably increased in 2,6-dialkyl derivatives. As seen from the spectral data, pyridine and phenyl rings in 2,6-diphenyl derivative 15 are not coplanar. The effect of 4-alkyl substituent is of hyperconjugative chacter. In general, the amount of the positive charge at C-4 in 2,6-dialkyl substituted salts is higher as compared to 2-monosubstituted compounds.     

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.     

Assignments of the 13C NMR Spectra of Enhydrin and 2′,3′-Dehydromelnerin A and the Molecular Structure of Enhydrin

Abstract

Two melampolide-type sesquiterpene lactones, enhydrin and 2,′ 3′-dehydromelnerin A, were isolated from a Louisiana population of Polymnia uvedalia. Their ¹³C NMR spectra were assigned using ¹³C-¹H correlation, DEPT and COLOC experiments. The molecular structure of enhydrin was established by single crystal X-ray diffraction.     

Kinetics of 1H→13C NMR cross-polarization in polymorphs and solvates of the antipsychotic drug olanzapine

The (1)H→(13)C NMR cross-polarization (CP) was studied under magic-angle spinning at 7.5 kHz in various crystal forms of the antipsychotic drug olanzapine: two polymorphs (metastable I and stable II) and eight solvates containing organic solvent and water molecules. The CP kinetics followed the non-classical I-I(*)-S model, in which CP begins in a spin cluster of proximate abundant spins I(*) and rare spins S, then is controlled by spin diffusion of the abundant spins I from bulk to the I(*) spins of the spin cluster and finally is governed by spin-lattice relaxation of the abundant spins in the rotating frame. The corresponding CP kinetics parameters were determined and analyzed. It was demonstrated that the, λ and T(df) values (the CP time constant, the cluster composition parameter and the (1)H spin-diffusion constant, respectively) were very useful to discriminate the functional groups, especially in the 3D parameter space. In order to conveniently analyze the large amount (175) of the collected CP parameters, the number of the observed variables was reduced using the principal component (PC) analysis. The 2D plot of PC2 vs. PC1 showed adequate separation of the CH(3), CH(2), CH and C cases (C stands for carbons without adjacent hydrogens). It was demonstrated that those cases were located along the PC1 axis in the order of increasing (1)H-(13)C dipolar couplings: C相似文献   

2(1H)喹啉酮化合物及其开环衍生物的13C NMR研究

本文报道了16种2(1H)喹啉酮及其开环衍生物的碳谱研究,归属了取代喹啉酮母核骨架及侧链上每个碳原子的化学位移,并就卤素取代对母核骨架碳的化学位移影响规律进行了探讨.文中所有化合物的核磁数据迄今未见文献报道.     

13C Nuclear Magnetic Resonance Studies of the Conformations of Serine‐3′‐ and 5′‐Thymidine Monophosphate Conjugates

The differences in the backbone conformation between O‐thymidine‐3′‐(1) and 5′‐yl O‐alkyl N‐phosphoryl serine methyl esters (2) have been investigated by solution ¹³C NMR spectroscopy. The stereo‐sensitive vicinal ³¹P–¹³C coupling constants were measured and used in the conformational analysis for the P–O5′–C5′, P–O3′–C3′, and P–N–C_α bonds. Three‐dimensional structural characteristics of dephosphorylation reactions of Compounds are also discussed.     

高碳糖希夫碱的1H NMR和13C NMR全归属

对7个高碳糖希夫碱进行了¹H和¹³C NMR检测，通过DEPT和¹H-¹H COSY，HMQC，HMBC等2D NMR 技术对其¹H和¹³C NMR数据进行了全归属和较详细的解析，并指出其NMR特征.     

洛莫司汀的1H、13C NMR全归属

应用~1H NMR、~(13)C NMR、DEPT135、~1H-~(13)C HMBC、~1H-~(13)C HSQC、~1H-~1H COSY和~1H-~1H NOESY等多种NMR技术,对文献报道的洛莫司汀(Lomustine)~1H和~(13)C NMR数据进行了修正与补充;特别是应用2D NMR对重叠程度较高的环己烷区进行了指认归属,并确定了其空间构型.     

Infrared Spectroscopic Study of Td‐Type Piperazinemetal(II) Tetracyanometallate(II) Benzene(1/1) Clathrates: Cd(C4H10N2)Cd(CN)4·C6H6 and Cd(C4H10N2)Hg(CN)4·1,25 C6H6

Abstract

The title compounds have been prepared in powder form. Their spectral data have been compared with those of the corresponding host complexes and found to be consistent with the host structure found in T_d‐type clathrates.     

一种热转印色素的1H、13C NMR研究

报道了一种热转印色带用黄染料的¹H、¹³C NMR , 应用¹H NMR、¹³C NMR、定量碳谱、DEPT、¹H-¹H COSY、HMQC、HMBC等确定了其在氘代氯仿中的分子结构, 并对全部谱峰进行了归属, 探索了黄染料在氘代氯仿中的结构对¹³C、¹H NMR谱图化学位移及谱峰裂分的影响.      

Concentration‐Dependent Variation of 1H‐NMR Chemical Shifts of Aromatic Protons in Sampangine Derivatives

A concentration dependence of the ¹H‐NMR chemical shifts of the aromatic protons in sampangine derivatives with a fused imidazole ring is observed. This variation is probably ascribable to self‐association of the molecules through an intermolecular π‐stacking interaction of the aromatic rings. The quantitative variation is correlated with the calculated electrostatic potential for these derivatives. The concentration variation appears to be independent of the nature of the substitution in the imidazole ring.     

1H, 13C and 15N NMR Studies of Protonation in Imidazo[1,2-α]Pyrimidine and Derivatives

We have studied1 the protonation behaviour of several cardiotonic polyazaheterocycles and recently shown that the 2-arylimidazo[l,2-a]pyrimidine (3a) undergoes protonation at the imidazo nitrogen (Nl). These investigations have utilised the shielding of acarbon nuclei and increases in ¹³C-¹H or ¹H-¹H couplings that occur on protonation of a heterocyclic nitrogen. We now report unequivocal protonation studies of the parent heterocycle, imidazo[1,2-a]pyrimidine (l), and its 2-aryl derivative (3b) which have allowed the effect of 2-aryl substitution on protonation to be determined. ¹⁵N NMR spectroscopy was employed to determine the protonation site of (1) in a titration study with H2SO4. In addition the N-methyl quaternary salts (21, (4) and (5) were prepared and ¹⁵N, ¹³C and ¹H chemical shifts measured so as to provide unambiguous substituent effects uncomplicated by possible proton transfers.     

Synthesis and Characterization of Novel Poly(1‐Naphthylamine)‐Montmorillonite Nanocomposites Intercalated by Emulsion Polymerization

Nanocomposites of montmorillonite (MMT) with poly(1‐naphthylamine) (PNA) is investigated for the first time by emulsion polymerization using three different oxidants. Polymerization of PNA was confirmed by Fourier transformation infrared (FT‐IR) as well as UV‐visible spectra. The in situ intercalative polymerization of PNA within MMT layers was confirmed by FT‐IR, X‐ray diffraction, conductivity; scanning electron microscopy (SEM) as well as transmission electron microscopy studies. X‐ray diffraction revealed intercalated as well as exfoliated structures of PNA/MMT nanocomposites, which were compared with the reported polyaniline‐MMT nanocomposites. It was found that the increase in the concentration of PNA in the interlayer galleries of MMT led to destruction of the layered clay structure resulting in exfoliation of the nanocomposite. Conductivity of the nanocomposites was found to be in the range of 10^?3 to 10^?2 S cm^?1 which was found to be higher than the ones reported for polyaniline‐clay nanocomposites as well as PEOA‐OMMT nanocomposites at similar concentrations of intercalated species. The morphology of PNA/MMT nanocomposites was found to be governed by the nature of the oxidant used.     

Spectrophotometric and 27‐Al NMR Characterization of Aluminum(III) Complexes with l‐Histidine

Abstract

The complex formation between l‐histidine (HHis) and aluminum(III) ion in water solutions was studied by UV spectrophotometric and 27‐Al NMR measurements at 298 K. UV spectra were measured on solutions in which the total concentration of histidine was from 15.0 to 50.0 mmol/dm³ and the concentration ratio of histidine to aluminum was varied from 3∶1 to 10∶1 in the pH range between 4.2 and 6.0. The spectra were taken in the wavelength interval 240–340 nm. Nonlinear least‐squares treatment of the spectrophotometric data indicates the formation of the complexes Al(HHis)³⁺, Al(His)²⁺, Al(HHis)His²⁺, and Al₂(OH)His⁴⁺ with the overall formation constants β_p,q,r: log β_1,1,1=11.90±0.04, log β_1,1,0=7.25±0.08, log β_1,2,1=20.1±0.1, and log β_2,1,1=5.92±0.12 (p, q, r are stoichiometric indices for metal, ligand, and proton, respectively). ²⁷Al‐NMR spectra were taken on solutions with the concentration of aluminum 50 mmol/dm³ and that of histidine 250 mmol/dm³. In the pH interval 5.0–6.1, two resonances at 9.5 ppm and 12.0 ppm were assigned to Al(HHis)²⁺ and Al(HHis)(His)²⁺ (or Al(OH)(HHis)₂ ²⁺), respectively.