Isomere N-aryltetrazole—II: 1H- und 13C-NMR-spektren

The ¹H and ¹³C NMR spectra of some isomeric N-aryltetrazoles have been obtained. Compared with the 1-aryltetrazoles, the H-2′ of the 2-aryltetrazoles are found to be more deshielded; the C-2′ are more shielded, indicating a higher extent of interannular conjugation present in 2-aryltetrazoles. The different behaviour of the isomers is attributed to a loss of coplanarity in 1-aryltetrazoles due to steric hindrance. The results are analyzed in terms of the chemical reactivity of the isomers. The tautomeric equilibrium of tetrazole is discussed by means of the ¹J_13CH coupling constants of the N-phenyltetrazoles. Hence tetrazole exists in solution primarily as the 1H-tautomer.     

The assignment of the 1H and the 13C NMR chemical shifts of N-phenyl-2,4-dimethylbuta-1,3-diene-1,4-sultam

The assignment of the signals in the ¹³C and ¹H NMR spectra of N-phenyl-2,4-dimethylbuta-1,3-diene-1,4-sultam is difficult for the signal pairs C-2 and C-4, C-1 and C-3, (C-1)? H, (C-2)? CH₃ and (C-4)? CH₃. The ¹³C NMR spectrum recorded under gated decoupling conditions provide long-range couplings which make possible an unambiguous assignment of the ¹³C NMR signal pairs. Application of the ¹H CW off-resonance decoupling technique in recording the ¹³C NMR spectra enables the assignment information from the ¹³C NMR spectrum to be transferred to the ¹H NMR spectrum.     

1H, 13C, 15N and 195Pt NMR studies of Au(III) and Pt(II) chloride organometallics with 2‐phenylpyridine

¹H, ¹³C, ¹⁵N and ¹⁹⁵Pt NMR studies of gold(III) and platinum(II) chloride organometallics with N(1),C(2′)‐chelated, deprotonated 2‐phenylpyridine (2ppy*) of the formulae [Au(2ppy*)Cl₂], trans(N,N)‐[Pt(2ppy*)(2ppy)Cl] and trans(S,N)‐[Pt(2ppy*)(DMSO‐d₆)Cl] (formed in situ upon dissolving [Pt(2ppy*)(µ‐Cl)]₂ in DMSO‐d₆) were performed. All signals were unambiguously assigned by HMBC/HSQC methods and the respective ¹H, ¹³C and ¹⁵N coordination shifts (i.e. differences between chemical shifts of the same atom in the complex and ligand molecules: Δ^1H_coord = δ^1H_complex ? δ^1H_ligand, Δ^13C_coord = δ^13C_complex ? δ^13C_ligand, Δ^15N_coord = δ^15N_complex ? δ^15N_ligand), as well as ¹⁹⁵Pt chemical shifts and ¹H‐¹⁹⁵Pt coupling constants discussed in relation to the known molecular structures. Characteristic deshielding of nitrogen‐adjacent H(6) protons and metallated C(2′) atoms as well as significant shielding of coordinated N(1) nitrogens is discussed in respect to a large set of literature NMR data available for related cyclometallated compounds. Copyright © 2009 John Wiley & Sons, Ltd.     

Structural correlations for 1H, 13C and 15N NMR coordination shifts in Au(III), Pd(II) and Pt(II) chloride complexes with lutidines and collidine

¹H, ¹³C and ¹⁵N NMR studies of gold(III), palladium(II) and platinum(II) chloride complexes with dimethylpyridines (lutidines: 2,3‐lutidine, 2,3lut; 2,4‐lutidine, 2,4lut; 3,5‐lutidine, 3,5lut; 2,6‐lutidine, 2,6lut) and 2,4,6‐trimethylpyridine (2,4,6‐collidine, 2,4,6col) having general formulae [AuLCl₃], trans‐[PdL₂Cl₂] and trans‐/cis‐[PtL₂Cl₂] were performed and the respective chemical shifts (δ^1H, δ^13C, δ^15N) reported. The deshielding of protons and carbons, as well as the shielding of nitrogens was observed. The ¹H, ¹³C and ¹⁵N NMR coordination shifts (Δ^1H_coord, Δ^13C_coord, Δ^15N_coord; Δ_coord = δ_complex ? δ_ligand) were discussed in relation to some structural features of the title complexes, such as the type of the central atom [Au(III), Pd(II), Pt(II)], geometry (trans‐ or cis‐), metal‐nitrogen bond lengths and the position of both methyl groups in the pyridine ring system. Copyright © 2010 John Wiley & Sons, Ltd.     

1H, 13C and 199Hg NMR Studies of the Complexation of HgCl2 by Imidazolidine-2-Thione and its Derivatives

Abstract

Mercury(II) complexes of imidazolidine-2-thione and its derivatives have been synthesized and their ¹H, ¹³C and ¹⁹⁹Hg NMR spectra measured. HgCl₂ forms L₂HgCl₂ type complexes (where L = imidazolidine-2-thione and its derivatives). The NH group of the ligand is shifted downfield by about +1.37 ppm in the ¹H NMR after complexation. The C-2 carbon in the ¹³C NMR is shifted by—6.50 ppm for mono N-substituted ligands, but by—5.30 ppm for N,N''-disubstituted ligands. The ¹⁹⁹Hg NMR resonance is shifted by about—60 ppm for N-substituted ligands, but—140 ppm shifts were observed for N',N'-disubstituted ligands.     

Regioselective and Stereoselective Addition of Tetrazole Derivatives to Electron‐poor Acetylenic Esters in the Presence of Triphenylphosphine

Protonation of the highly reactive 1:1 intermediates produced in the reaction between triphenylphosphine and acetylenic esters by tetrazole derivatives leads to the formation of vinyltriphenylphosphonium salts. The cation of these salts undergoes an addition reaction with the counter anion in CH₂Cl₂ at room temperature to yield the corresponding stabilized phosphorus ylides. Elimination of triphenylphosphine from the stabilized phosphorus ylides leads to the corresponding electron‐poor N‐vinyl tetrazoles in fairly high yields. Structures of N‐vinyl tetrazoles were determined by IR, ¹H NMR, ¹³C NMR and single crystal X‐ray structure analyses. The reaction is fairly regioselective and stereoselective.     

1H, 13C and 15N NMR study of vinyltetrazolium salts and processes of their synthesis

The ¹H, ¹³C and ¹⁵N NMR spectra of several N- and C-vinyltetrazolium salts have been recorded and the observed chemical shifts together with the data of quantum-chemical calculations have been used for evaluation of electronic structure of the investigated substances and selectivity of the exhaustive alkylation of 1,5- and 2,5-substituted tetrazoles.     

Investigation of benzimidazoles. III—transmission of the substituent effects in 2-substituted 1-methylbenzimidazoles studied by 13C nuclear magnetic resonance

The influence of substituents on the ¹³C NMR chemical shifts of 2-substituted 1-methylbenzimidazoles has been investigated. The electronic effects of the substituents are transmitted to C-4 and C-7 mainly by the resonance mechanism, and to C-5, C-6 and N-CH₃, by approximately equal contributions of the resonance and inductive components. A critical analysis of the share in the transmission of substituent effects through the ‘pyridine-type’ and ‘pyrrole-type’ nitrogen atoms is given.     

Détermination par RMN 1H et 13C des Couplages J(CH) et J(CC) dans des Monomères Precurseurs de Lignine: Vanilline,Férulate d'Ethyle et Alcool Coniférylique Sélectivement Enrichis en 2H et 13C

Some monomer model compounds of lignin have been selectively ²H and ¹³C labelled: vanillin, ethyl ferulate, coniferyl alcohol and ethyl hydrogen malonate. Deuterium isotope effects on the ¹³C chemical shifts in [formyl-²H]vanillin, [5-²H]vanillin and [α,α,5-²H₃]coniferyl alcohol made the unambiguous assignment of the aromatic ¹³C signals possible. Absolute ^1,2,3J(CC) values have been determined on ¹³C spectra of [formyl-¹³C]vanillin, and of ethyl ferulate and coniferyl alcohol in which the vinylic C-γ and C-β carbons were ¹³C enriched. It has been possible to measure ⁴J(C?O, C-4) in vanillin and ⁴J(C-γ, C-4) in ethyl ferulate. The determination of ^1,2,3,4J (CH) absolute values was done by means of gated decoupled ¹³C spectra of the non-labelled compounds. When second order effects made the use of this technique impossible we determined certain J(CH) values and their signs either by analysing the ¹H NMR spectra of ¹³C labelled coniferyl alcohol [²J(C-β, H-γ), ²J(C-β, H-α), ²J(C-γ, H-β), ³J(C-γ, H-α)] or by a double irradiation experiment on the 250 MHz ¹H NMR spectrum of ethyl [β-¹³C] ferulate [for ²J(C-β, H-γ)].     

Carbon-13 NMR spectra of isocoumarin,N-methyl-1(2H)-isoquinolinone and related compounds

The ¹³C NMR spectra of isocoumarin, N-methyl-1(2H)-isoquinolinone and 14 of their 3- and/or 4-substituted derivatives were measured and assigned with the aid of various spectral techniques. The values of the one-bond and some of the long-range ¹³C-¹³C-¹H coupling constants are reported. The effect of substitution on the ¹³C chemical shifts is discussed.     

Geometrical isomerism and 13C spectra of the β-substituted Enones R1?C(1)O?C(2)HC(3)H?R2

The ¹³C chemical shifts of the unsaturated carbons were measured in 31 cis and trans pairs of β-substituted enones R₁? C(1)O? C(2)H?C(3)H? R₂. In these polarized ethylenes the chemical shifts of the olefinic carbons are simply related by the equation δ_c=δ_t+A. The steric and electronic effects introduced by the R₁ and R₂ substituents influence the chemical shifts of C-2 and C-3 in both isomers. It is shown that the sign and magnitude of the intercept A mainly reflect the π-charge electronic density changes which arise in the cis isomer and are transmitted via the π-framework. The effect of the steric interaction on the chemical shift of C-3 in the cis isomers is postulated to be related to the symmetry of the substituents. Therefore, the differential shielding of C-3 is indicative of the conformational structure of the cis molecule.     

Comprehensive 1H and 13C NMR assignment of 13 protobassic acid saponins

This study aimed to carry out complete ¹H and ¹³C NMR assignment of 13 protobassic acid saponins, including arganins A–C ( 1 – 3 ) and F ( 4 ), butyrosides B–D ( 5 – 7 ), tieghemelin ( 8 ), 3′-O-glucosyl-arganin C ( 9 ), Mi-saponins A–C ( 10 – 12 ), and mimusopsin ( 13 ), recorded in methanol-d₄. This was accomplished by the analysis of high-resolution one-dimensional (1D) NMR (¹H and ¹³C), two-dimensional (2D) NMR (¹H–¹H COSY, HSQC, and HMBC), and selectively excited 1D TOCSY spectra. Before this study, ¹H and ¹³C NMR data of arganins A–C ( 1 – 3 ) and F ( 4 ) were partially assigned. Our effort leads to their complete assignment, especially the glycon residue, and revises some reported data. Some revisions of the ¹H and ¹³C NMR data in the glycon part of butyroside C ( 6 ), tieghemelin ( 8 ), Mi-saponin A ( 10 ), and mimusopsin ( 13 ) were made. Those data of butyrosides B and D ( 5 & 7 ) and Mi-saponin B ( 11 ), which had not been recorded in methanol-d₄, are provided. In addition, the ¹H and ¹³C NMR data of Mi-saponin C ( 12 ) are reported for the first time. These data, being recorded in methanol-d₄, should be more friendly for use as a reference for identifying the related triterpenoid saponins.     

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.     

Triple 13C-{1H, 2H} NMR: A precise quantitative method for study deuterated organic compounds

We have shown the advantages of quantitative ¹³C-{¹H, ²H} NMR spectroscopy in the study of deuterated organic compounds. The simultaneous use of two saturating fields at the resonance frequencies of protons and deuterons significantly simplifies NMR spectra and increases the sensitivity of the method. We tested the performance capabilities of triple resonance when analyzing the mixture of tetradecane isotopomers and precisely measuring the isotope shifts Δ(¹³C) for biphenyl-d₅.     

Investigation of substituent effects on the 1H and 13C NMR spectra of (Z)-N-(arylmethylene)-arylamine N-oxides (α,N-diaryl nitrones)

Substituent effects on the ¹H and ¹³C chemical shifts of 18 differently substituted (Z)-α,N-diaryl nitrones [N-(p-X-benzylidene)phenylamine N-oxides (Series I) and N-(benzylidene)-p-Y-phenylamine N-oxides (Series II)] have been obtained. A correlation has been found between the chemical shifts of the azomethine proton (H-α) and the Hammett σ parameters and the Swain and Lupton F and R parameters. Correlations of the chemical shifts of C-1 and C-4′ in Series I, and of C-α and C-1′ in Series II, with the same parameters have been investigated. In addition, the chemical shifts of the aromatic protons and carbons of the p-disubstituted (m-disubstituted in one case) benzene rings correlated with the appropriate substituent increments (Z_i). These correlations confirm the dual behaviour of the nitrone group and the presence of through-resonance in these nitrones.     

Carbon-13 NMR spectra of saturated heterocycles: XI—Tetrahydropyrans (oxanes)

The ¹³C NMR spectra of 62 oxanes (tetrahydropyrans) with and without methyl substituents at various ring positions, some of them bearing in addition (or instead) ethyl, vinyl, ethynyl, carbomethoxy and methylol substituents at C-2, have been recorded, and the 294 resulting chemical shifts have been correlated by multiple linear regression analysis. Axial and equatorial α-, β-, γ-, δ-, gem- and vic-parameters for shifts caused by methyl groups at all ring positions, and similar parameters for Et,—CH?CH₂,—C?CH, CO₂Me and CH₂OH groups at C-2, are reported. Standard deviations of the parameters are, in most cases, within 0.3 ppm and the agreement of calculated and experimental shifts is excellent. This is probably the largest parameter set of this type extant. ¹³C NMR spectra of a number of additional substituted tetrahydropyrans, and of 3,6-dihydro-2H-pyrans and 3,4-dihydro-2H-pyrans, are tabulated and discussed.     

Sels de Pyrylium. XVIII. Etude par RMN du Carbone-13 de Sels d'Aminopyrylium et des Barrières de Rotation dans quelques Cations N,N-Diméthylaminopyrylium

The C-2—N bond of 2-N,N-dimethylaminopyrylium cations has a partial π character due to the conjugation of the nitrogen lone-pair with the ring. The values of ΔG^≠, ΔH^≠, ΔS^≠ parameters related to the corresponding hindered rotation have been determined by ¹³C NMR total bandshape analysis. This conjugation decreases the electrophilic character of carbon C-4 so that the displacement of the alkoxy group is no longer possible. Such a hindered rotation also exists in 4-N,N-dimethylaminopyrylium cations and the corresponding ΔG^≠ parameters have been evaluated. Comparison of these two cationic species shows that hindered rotation around the C—N bond is larger in position 4 than in position 2. Furthermore, the barrier to internal rotation around the C-2? N bond decreases with increasing electron donating power of the substituent at position 4. ΔG^≠ values decreases from 19.1 kcal mol^?1 (79.9 kJ mol^?1) to 12.6 kcal mol^?1 (52.7 kJ mol^?1) according to the following sequence for the R-4 substituents: -C₆H₅, -CH₃, -OCH₃, -N(CH₃)₂.     

Synthese und NMR-Spektren einiger 13C-markierter Thio- und Seleno-äther, -acetale und -orthoester

Synthesis and NMR Spectra of Some ¹³C-Labelled Thio- and Seleno-ethers, -acetals, and -orthoesters Twenty-seven different open-chain and cyclic derivatives (RX)_nCH_4-n and (RX)_nCH_3-nR′ with n = 1?3, X = S or Se, R,R′ = alkyl or aryl, 1,3,5-trithiane, and bis-(dimethylsulfonio)methane and -methanide with single or multiple ¹³C-labelling have been synthesized. The ¹³C-NMR spectra of the sulfur and selenim compounds have been measured, and the dependence of the chemical shifts (δ_c) and coupling constants [′J(C,H), ′J(Se,C)] from the substitution pattern in discussed (Fig. 1) and compared with the polyhalogeno-methanes (Fig. 2).     

13C NMR spectra of non-labelled and 15N-mono-labelled azo dyes

¹³C NMR spectra of four types of azo coupling products from benzenediazonium chloride have been measured and interpreted, viz. hydrazo compounds with an intramolecular hydrogen bond (3-methyl-1-phenylpyrazole-4,5-dione 4-phenylhydrazone), azo compounds without an intramolecular hydrogen bond (4-hydroxyazobenzene), azo compounds with an intramolecular hydrogen bond (2-hydroxy-5-tert-butylazobenzene) and an equilibrium mixture of both the tautomers of 1-phenylazo-2-naphthol. The absolute values of the J(¹⁵N¹³C) coupling constants have been determined by recording the spectra of the ¹⁵N isotopomers, and have been used, in some cases, for ¹³C signal assignment. A relationship has been found between the chemical shifts of the C-1′ to C-4′ carbons of the phenyl group (from the benzenediazonium ion) or the ¹J(¹⁵N¹³C) coupling constant, and the composition of the tautomeric mixture.     

13C-NMR-Untersuchungen zur Strukturaufklärung von Polysacchariden und deren Methylderivaten

The ¹³C NMR spectra of some polysaccharides and their methyl derivatives have been analysed. The numbers and positions of the assigned ¹³C NMR signals give some information about the structure of the monomer unit and the positions of the glycosidic linkage but no information about the anomeric configuration. In this case the ¹J(C-1, H) coupling constants make it possible to identify the anomeric configuration, because the mean differences of the J values for the α- and β-anomers are 12 Hz (at least 5 Hz) with the higher values for the α-anomers.