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.     

A Study of the behaviour of an analogous series of 2H-thiopyrans, 6H-1,3-thiazines and their derivatives by carbon-13 and nitrogen-15 nuclear magnetic resonance

The influence of substituents in a new series of 2H-thiopyrans, 2H-thiopyran-2-ones (thiones) and their thiazine analogues is examined by means of carbon (¹³C) and nitrogen (¹⁵N) NMR. A linear relationship is shown to exist between the chemical shifts (δ_13C or δ_15N) of the thiopyrans and the thiazines. This relationship is a good indication of the structural similarity which exists between the two series.     

RMN 13C d'α alcoxy-indenes et d'α alcoxy-styrenes : Topologie electronique du systeme Π et une reflexion sur la relation entre deplacement chimique et reactivite dans les ethers d'enol

¹³C NMR chemical shifts of ethylenic carbon atom C_β of α alkoxy-indenes and α-alkoxy-styrenes are affected by the conformation of the OR group with respect to the double bond and hence the efficiency of p- Π conjugation but, contrary to previous results, δC_α is not affected. The phenyl group exerts a diamagnetic Π- effect on C_α and C_β which is a function of its dihedral angle with the double bond. Although δC_β is especially sensitive to the Π-electron density, the chemical shifts of the ethylenic carbons are best understood by considering the total charge density. The σ and Π contributions to the total charge density are discussed using the preferred conformation of the molecules. This approach strongly suggests that the correlation between the gradual shift of δC_α to low frequency and the gradual shift of δC_β to high frequency (relative to TMS) as R changes from RCH₃ to RtC₄H₉ in certain series of enol-ethers is not due to pΠ conjugation variations. This method of interpreting ¹³C NMR shifts, as opposed to previous methods, is compatible with explanations of other physico-chemical properties of alkyl vinyl ethers. Although it is sometimes possible to correlate the gradual shifts of δC_β with (σ + Π) electron density variations in a homogeneous series, it seems impossible to predict the relation. In all cases, there is no evident correlation between gradual shifts of δC_β(orδC_α) and the reactivity of enol ethers because one cannot consider the role of the out-of-plane conformation of the alkoxy group (which increases from RCH₃ to RtC₄H₉); however, the out of plane conformation does not have an identical effect on δC_β and the reactivity.     

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.     

Solvent-Induced Deuterium Isotope Effects in 13C- and 15N-NMR. Spectra of Enaminones

The effect of deuterium on the ¹³C and ¹⁵N chemical shifts of enaminones has been investigated. D/H isotope shifts are reported for neutral and protonated species, i.e., when the isotope is exchanged on the C(2)-, N-, or O-atoms. In cases of slow exchange the isotope shifts were obtained from solutions containing both isotopomers, whereas for fast exchange (acidic solutions) either separate NMR. sample tubes (¹⁵N-NMR.) or coaxial tubes (¹³C-NMR.) were used. In neutral molecules the isotope effects δ_C(D, H) are intrinsic in nature. In acidic solutions, the enaminocarbonyl cations formed exhibit δ_C(D, H)- and δ_N(D, H)-values which are discussed in terms of the proton transfer. The mesomeric character of the cations is reflected by characteristic features in the δ_C(D, H)- and δ_N(D, H)-values, which can be ascribed to isotopic perturbation of resonance. O-Protonation shifts in the ¹⁵N-resonance, observed for the first time, are large and positive (+60 to +76 ppm), in contrast to amides, where the effects are of the same sign but an order of magnitude smaller. Both protonation shifts and solvent-induced isotope effects are discussed in connection with the nucleophilic character of the reactive centers in the enaminone synthon.     

13C and 29Si chemical shifts and coupling constants involving tris[(trimethylsilyl)methyl] silicon compounds

Silicon-29(δ²⁹Si) NMR chemical shifts are reported for the first time of tris[(trimethylsilyl)methyl] silicon compounds (disilylated derivatives) (Me₃Si^A)₃ C_αL, where L = Si^BR₁R₂R₃ and where R varies widely in electronegativity. ²⁹Si chemical shifts exhibit good correlation with the electronegativities of the groups bonded to the silicon atom. The ¹³C NMR spectra of these compounds have been recorded and assigned. δ¹³C_α is shown to depend on the type of substitutent on Si^B. The variation of ²⁹SiH coupling constants with electronegativity of R is studied.     

Bor-Stickstoff-Verbindungen,LXVIII [1]. Kernresonanzspektroskopische Untersuchungen an 1,3,2-Diazaboracycloalkanen und Phenylboranderivaten

Boron-Nitrogen Compounds. LXVIII. Nuclear Magnetic Resonance Studies on 1,3,2-Diazaboracyloalkanes and Phenylborane Derivatives The ¹H chemical shift differences Δδ = δ (NCH ₂) – δ (NCH ₃) of 1,3-dimethyl1,3,2-diazaboracycloalkanes as well as the corresponding differences of ¹³C chemical shifts are dependent upon the ring size. No simple correlation exists between δ_11B and δ_13C of the boron-bonded phenyl carbon atom of phenylborane derivates, although stereochemical factors appear to influence the absolute values of δ_13C. ¹³C Nuclear resonance measurements permit the observation of conformational isomers of bis(methylamino)phenylborane and N-trimethyl-B-triphenylborazine at low temperatures and confirm the pseudoarmatic nature of the 1,3,2-diazaboroline ring system.     

n-π-Interaction in Enamines and Enaminoketones. A 15N-NMR. Study

¹⁵N-Chemical shifts of 32 enamines, 11 enaminoketones and 28 closely related amines have been determined with the isotope in natural abundance. In order to eliminate substituent effects, differential chemical shifts Δδ(N) are defined as δ_N(amine)-δ_N(enamine). This parameter is shown to correlate well with the free enthalpy of activation ΔG# for restricted rotation about the N? C(α) bond in enamines with extended conjugation. Δδ(N) values of substituted anilinostyrenes correlate also with ¹³C-chemical shifts of the β-carbon in the enamine system and with Hammett σ-constants of the aniline substituents. The experimental results suggest that differential ¹⁵N shifts are a useful probe to study n, π-interaction in enamines.     

The use of MM/QM calculations of 13C and 15N chemical shifts in the conformational analysis of alkyl substituted anilines

The calculation of the ¹³C and ¹⁵N NMR chemical shifts by a combined molecular mechanics (Pcmodel 9.1/MMFF94) and ab initio (GIAO (B3LYP/DFT, 6-31 + G(d)) procedure is used to investigate the conformations of a variety of alkyl substituted anilines. The ¹³C shifts are obtained from the GIAO isotropic shielding (Ciso) with separate references for sp³ and sp² carbons (δc = δref − Ciso). The ¹⁵N shifts are obtained similarly from the GIAO isotropic shielding (Niso) with reference to the ¹⁵N chemical shift of aniline. Comparison of the observed and calculated shifts provides information on the molecular conformations. Aniline and the 2,6-dialkylanilines exist with a rapidly inverting symmetric pyramidal nitrogen atom. The 2-alkylanilines have similar conformations with the NH₂ group tilted away from the 2-alkyl substituent. The N,N-dialkylanilines show more varied conformations. N,N-dimethylaniline has a similar structure to aniline, but N-ethyl, N-methylaniline, N,N-diethylaniline, and N,N-diisopropylaniline are conformationally mobile with two rapidly interconverting conformers. In contrast, the anilines substituted at C₂ and the nitrogen atom exist as one conformer where the steric interaction between the C₂ substituent and the N substituent determines the conformation. In 2-methyl-N-methylaniline, the nitrogen atom is pyramidal as usual with the N-methyl opposite to the 2-methyl, but in 2-methyl-N,N-dimethyl aniline, the NMe₂ group is now almost orthogonal to the phenyl plane. This is also the case with 2-methyl-N,N-diethylaniline and 2,6-diisopropyl-N,N-dimethylaniline. The comparison of the observed and calculated ¹⁵N chemical shifts confirms the above findings, in particular the pyramidal conformation of aniline and the above observations with respect to the conformations of the N,N-dialkylanilines.     

Zur Interpretation 29Si-NMR-chemischer Verschiebungen

The ²⁹Si-NMR chemical shifts δ(²⁹Si) of (CH₃)_4?nSiX_n compounds and some ¹³C-NMR chemical shifts δ(¹³C) of analogous carbon compounds are discussed by means of relative paramagnetic screening constants σ*, calculated by a simplified model. In this model only the Si(3P)- and C(2P)-orbitals are considered; for the calculations, the electronegativities of Si, C and the X-substituents and a single empirical parameter are necessary. The calculated values of σ* are in good agreement with the change of the chemical shifts which are observed for the (CH₃)_4?nMX_n compounds with different X and n. These results clearly show that δ(²⁹Si) and δ(¹³C) depend primarily on the σ-charge of the Si- and C-atom, and that (P? d)π-interactions on the Si-atom are of minor importance.     

13C NMR chemical shift and electronic structure of polyoxymethylene in the solid state

High-resolution ¹³C NMR spectra of polyoxymethylene (POM) in the solid state have been measured in order to obtain a relationship between the conformation and ¹³C NMR chemical shift tensor (δ₁₁, δ₂₂ and δ₃₃) and its isotropic average. It was found that the ¹³C isotropic chemical shift of POM in the crystalline region appears upfield with respect to that in the noncrystalline region and that the width Δδ ( = δ₁₁ - δ₃₃) in the crystalline region is much larger than that in the noncrystalline region. These experimental findings can be reasonably explained by a theoretical calculation for an infinite POM chain based on a tight-binding molecular orbital calculation within the CNDO/2 framework.     

1H and 13C NMR study of the enol–enolic tautomerism of some cyclic β-ketoaldehydes

Aldehyde (δCH) and enolic (δOH) proton chemical shifts, the corresponding spin–spin coupling constants (JCH,OH) and the ¹³C chemical shifts (δC) have been measured for three cyclic β-ketoaldehydes as a function of temperature. A tautomeric equilibrium has been shown to exist between the aldo–enol ( A ) and hydroxymethylene ketone ( B ) forms. The chemical shifts δCH δOH and δC for the two pure tautomeric forms A and B have been calculated. The enthalpy changes ΔH in the tautomeric process A ? B and the percentages of the tautomeric forms have been determined.     

Theoretical Study of 13C Chemical Shifts Structures of Some ortho-Substituted 3-Anilino-2-nitrobenzo[b]thiophenes and 2-Anilino-3-nitrobenzo[b]thiophenes and Comparison with Experimental

¹³C NMR chemical shifts have been calculated for structures of some substituted 3‐anilino‐2‐nitrobenzo‐[b]thiophenes ( 2 o) and 2‐anilino‐3‐nitrobenzo[b]thiophenes ( 3 o) derivatives containing OH, NH₂, OMe, Me, Et, H, F, Cl and Br. The molecular structures were fully optimized using B3LYP/6‐31G(d,p). The calculation of the ¹³C shielding tensors employed the GAUSSIAN 03 implementation of the gauge‐including atomic orbital (GIAO) and continuous set of gauge transformations (CSGT) by using 6‐311++G(d,p) basis set at density functional levels of theories (DFT). The isotropic and the anisotropy parameters of chemical shielding for all compounds are calculated. The predicted ¹³C chemical shifts are derived from equation δ=δ₀+δ where δ is the chemical shift, δ is the absolute shielding, and δ₀ is the absolute shielding of the standard TMS. Excellent linear relationships have been observed between experimental and calculated ¹³C NMR chemical shifts for all derivatives     

15N, 31P,and 13C NMR Spectroscopy of N-Arylsulfonyl-and N-Arylcarbonyl-P,P,P-triphenylphospha-λ-Azenes. Substituent Effects and Electronic Structure

Abstract

The ¹⁵N, ³¹P and ³¹C NMR spectra of several series of phospha-λ⁵-azenes are reported. For the N-arylsulfonyl-P,P,P-triphenylphospha-δ⁵-azene series (R-C₆H₄N-SO₂-PPh₃), the ³¹P chemical shifts, various ¹³C chemical shifts and ¹J_PN were observed to correlate linearly with the Hammett σ constants. Interestingly, the ¹⁵N chemical shifts did not correlate acceptably with any σ or with the Taft dual substituent parameter equation, and 1J_PC was invariant with substituent. For the N-arylcarbonyl-P,P,P-triphenylphospha-λ⁵-azene series (R-C₆H₄-CO-N=PPh₃), δ_31P and various δ_13C's were observed to linearly correlate with the δ constants, while δ_15N, ¹J_PN and ¹J_PC correlated with both the σ and σ constants. For the N-phenyl-P,P,P-triarylphospha-λ⁵-azene series [Ph-N=P(C₆H₄-R)₃] the best correlations were observed between ³¹P, ¹⁵N and several ¹³C chemical shifts and the σ constants.     

Some observations on the relationship between charge and 13C chemical shift in cyclohexadienylic anions and cations

Carbon-13 chemical shifts δ^± in a variety of cyclohexadienylic cations and anions have been separated semi-empirically into contributions from (a) the hypothetical neutral framework, (b) charge effects and (c) interactions between ions and between ions and solvent molecules. Carbon-13 shifts for sites in neutral model compounds, δ⁰, approximate contribution (a) the shift differences for the model carbons δ^±_3,5-δ⁰_3,5 are assumed to reflect electric field effects (b). Thus what remains, δ^±_s-δ⁰_s- (δ^±_3,5-δ⁰_3,5) comes from the charge. The summation of these terms for each of the ions comes to ca. 165 ppm. This shows that a changein charge of ±1 of the neutral model, with correction for the electric field, brings about a change in shift of 165 ppm, thus supporting the linearity of charge with shift.     

Carbon-13 NMR spectra of coumarin and methoxycoumarins—a reinvestigation of charge density/Chemical Shift Relations

The carbon-13 NMR spectra of coumarin, 6-, 7-, 8-methoxycoumarin, and 5,7-, 7,8-, 5,8- and 6,7-dimethoxycoumarin have been measured and assigned. It is shown that substituent induced chemical shifts S(δ) in the mono- and disubstituted systems correlate well with the HMO atom-atom polarisibilities π_ij of the parent compound: S_i(δ_i) = 80.13 π_ij with a standard deviation of 1.42 ppm and a correlation factor of 0.994. Correlations between δ(¹³C) values and charge densities calculated by various semi-empirical methods are less successful.     

NMR- und schwingungsSpektroskopische Untersuchungen höherer Indiumtrialkyle

NMR and Vibrational Spectroscopic Investigations on Higher Indium Trialkyls Several isomeric indium tripentyles and trihexyles are synthesized by known methods. The chemical shifts δ of the ¹³C NMR spectra are used together with those of the corresponding alkanes for determining the increments Δδ(¹³C) = δ(InR₃)–δ(RH). By means of these increments and the Grant/Paul-method the chemical shifts δ(¹³C) of any indium trialkyl can be calculated. The vibrational spectra (IR and Raman) of most liquid trialkyls show very obvious rotameric splittings of the InC vibrations between 450–600 cm^?1. Both frequent conformations of the alkyl ligands with three and more C atoms consist of either a βH atom (notations P_H, S_HH, and T_HHH with vInC between 450–500 cm^?1) or a γC atom (P_C, S_CH, T_CHH with vInC between 550–600 cm^?1) in the transposition to indium. The InC stretching modes of all other more rare configurations can be observed between 500 to 550 cm^?1.     

1H- und 13C-NMR-Untersuchungen zur Struktur N-substituierter Tetrazole—Die Strukturen des N-Methoxycarbonyl-, N-Acetyl- und N-(Tri-n-butylstannyl)-tetrazols sowie Substituenteneffekte auf δ13C und 1J(CH)

The ¹H and ¹³C NMR spectra of several isomeric N-substituted tetrazoles have been investigated. ¹³C NMR is shown to be more useful for distinguishing between structural isomers of N-substituted tetrazoles except for those carrying electropositive substituents like SnBu₃. Correlations of δC-5 (inverse) and ¹J(C-5,H) with s?₁ found for 1-substituted tetrazole allowed the identification of the N SnBu₃ derivative as 1-(tri-n-butylstannyl)tetrazole. The phenyl carbon chemical shift difference ΔC′ = δC-3′-δC-2′ is insignificant for structure elucidation and conformational studies of N-substituted 5-phenyltetrazoles; ΔH′ from ¹H NMR spectra seems to be more useful.     

Beziehungen zwischen chemischer Verschiebung und Ladungsdichte

This work is concerned with the relationship between chemical shifts (δ) of protons and their charge densities (q). It can be shown that the relation δ^H = a + bq^H + cq^C (q^C = charge density at the corresponding C-atom) fits best for a prediction of δ-values from calculated charge densities. The smallest standard error for the prediction of δ-values is obtained if the charge densities are calculated by the CNDO- or INDO-method.