Structural characterization of polybenzyls by high field 13C-NMR spectroscopy

¹³C-NMR Spectroscopy has been used for the structural characterization of polybenzyls synthesized from the polymerization of benzyl chloride catalyzed by arene chromium tricarbonyls. The ¹³C-chemical shifts for various mono-, di-, tri-, and tetrasubstituted phenyl groups in a polybenzyl have been calculated by the use of additivity parameters and compared with their observed shifts. Although from a theroetical point of view, polysubstitution on a phenyl ring gives rise to a number of isomers, the results indicate the preferential formation of only a few of them due to steric and electronic considerations. Based on quantitative ¹³C-NMR data, several important structural parameters including the percentage of mono-, di-, tri-, and tetrasubstituted phenyl rings in the polybenzyl can be calculated. The extent of branching in a number of polybenzyls prepared under different experimental conditions was determined. The results indicate an increase in branching with the increase in reaction temperature.     

Über polygermane: XI. Funktionalisierung von hexaphenyldigerman

The optimum conditions for selectively cleaving off two phenyl groups in Ge₂Ph₆ by trichloroacetic acid have been determined. Neither trihaloacetic acids nor HCl/AlCl₃ nor reactive tetrahalides MCl₄ are suitable reagents for cleaving one phenyl group alone. The ¹³C NMR chemical shifts of functional phenyl-mono- and -digermanes are given. The crystal structure of 1,2-bis(trichloroacetate)tetraphenyldigermane has been determined and refined to R = 0.048. The digermane bond is bridged by both acetates (distances GeGe 239.3(2), GeO 207.3(3) and 231.4(3) pm). The Ge atoms have trigonal bipyramidal coordination.     

13C-NMR.-Substituenteninkremente der N3-Gruppe in Azido-1,4-benzochinonen

¹³C-NMR. Substituent Increments of the Azido-group in 1,4-Benzoquinones The empirical substituent increments of the azido-group in 1,4-benzoquinones have been derived from the ¹³C-NMR. chemical shifts of 2-azido-5-chloro-1,4-benzoquinone. The validity of the obtained values was tested by comparison of the empirical and computed ¹³C-NMR. chemical shifts of other azido-chloro-1,4-benzoquinones.     

13C-NMR Study of Anomalous Linkages in Polyurethane

Several kinds of model compounds for anomalous linkages in polyurethanes (branching or crosslinking; allophanate and biuret) were prepared. The phenylisocyanate (PHI) based models were identified by IR and NMR. The ¹³C-NMR chemical shifts effects due to the anomalous linkages were determined. The 4,4′-diphenylmethane diisocyanate (MDI) based models were purified incompletely but the characteristic signals of the aromatic carbons were nevertheless found in their spectra. Two types of segmented polyurethane (SPU) were prepared and the anomalous linkages were investigated by ¹³C-NMR. The signals due to the allophanate (Al) and the triphenylbiuret (TB) linkages were observed in the spectra of the SPU prepared at high temperature (>80°C) or prepolymer gels yielded by abnormal reaction. A small signal due to a phenyl carbon of biuret (Bi) linkage was observed even in a normally prepared SPU (polyetherurethane-urea). Employing the phenyl carbon signals was advantageous for the determination of anomalous linkages because of their larger intensities.     

Hyperfine shifts of the 13C-NMR. in low spin iron(3) porphyrin complexes

The ¹³C-NMR. in Zn(II)(Porphin), Fe(III)(Porphin)(CN₂), Zn(II)(Tetraphenyl-porphin), and Fe(III)(Tetraphenylporphin)(CN₂) have been identified, and the ¹³C hyperfine shifts in the iron complexes evaluated. It was found that dipole-dipole coupling with the electron spin localized in the π-orbitals of the aromatic carbon atoms makes an important contribution, to the ¹³C hyperfine shifts. In a preliminary analysis the experimental spin density distribution obtained from the combined ¹H- and ¹³C-NMR.-data is compared with theoretical models of the iron porphyrin complexes.     

Einfluss der Orientierung von Substituenten auf die chemische Verschiebung von 13C. II. 13C-NMR.-spektroskopische Untersuchung von substituierten Spiro [cyclopropan-1′,9-fluorenen]

Effect of the Orientation of Substituents on the Chemical Shift of ¹³ II. ¹³C-NMR. Study of Substituted Spiro [cyclopropane-1′, 9-fluorenes] The ¹³C-NMR. spectra of spiro[cyclopropane-1′, 9-fluorenes] substituted at the cyclopropane ring have been assigned, largely with the aid of selective proton decoupling. The effects of the substituents upon the chemical shifts of the aromatic carbons are orientation dependent. the effects of cis-substituents on γ-carbon atoms are large and negative (inducing high field shifts), those of trans-substituents smaller and dependent on the electron donor/acceptor properties of the substituents. The effects on δ-carbon atoms in close proximity of the substituents are large and positive; they are interpreted in terms of electric field effects.     

Zur Kenntnis des Chinoiden Zustandes—XX: 13CMR-Untersuchungen an Cyclohexadienonen

The ¹³C-NMR-chemical shifts of 19 para- and 5 ortho-cyclohexadienones are determined by ¹³C-Fourier-transformation spectroscopy and assigned. The effect of substituents on the chemical shift of the ring carbon atoms is discussed. The mutual dependence of the shifts of the olefinic ring carbons and the allylic carbon atom in the para-quinolid ring system is shown by computing regression lines. A frequently observed correlation between ¹³C-NMR and ¹H-NMR is examined in the case of cyclohexadienones.     

Résonance Magnétique Nucléaire de 17O. Aldéhydes et cétones aliphatiques: additivité des effets de substitution et corrélation avec la 13C-RMN

¹⁷O-NMR. Aliphatic aldehydes and ketones, additivity of substituent effects and correlation with ¹³C-NMR. The ¹⁷O-chemical shifts of 9 aldehydes, 22 aliphatic and 4 alicyclic ketones, in the natural abundance FT.-NMR. spectra followed a good correlation with the ¹³C-chemical shifts of the terminal C-atoms of corresponding methylene compounds. An additivity relation involving 6 parameters represents the ¹⁷O-shifts of 28 of the measured products with a standard deviation of 2.5 ppm. The additivity parameters are discussed with respect to the modifications of the polarity of the carbonyl group induced by the hyperconjugative interaction of π and π* orbitals with the πCH ₃ orbitals of the alkyl substituent groups.     

13C-NMR.-Spektren N-acylierter Indoline. Einfluss der Orientierung der Carbonylgruppe auf die chemische Verschiebung

¹³C-NMR. spectra of N-acylated indolines. Effect of the orientation of the carbonyl group on the chemical shift Large downfield shifts are observed in the ¹³C-NMR. spectra of indolines and related compounds induced by electric field effects of carbonyl and oxime groups.     

Etude par Résonance Magnétique Nucléaire de dérivés anthracéniques: II—Anisotropie magnétique du phényle et effets steriques

The peri effect induced by the phenyl group has been studied in the anthracene series by means of ¹H and ¹³C n.m.r. The chemical shifts of overcrowded protons can be explained by a combination of magnetic anisotropy and steric effects. Steric contributions amount to c. 25% of the phenyl induced shift at the peri position. Amongst published ring-current theories, only the model of Johnson and Bovey is capable of describing correctly the shielding region of the phenyl group. The unexpected shieldings and deshieldings, observed by ¹³C n.m.r. in the case of very hindered derivatives, is probably due to distortions of the anthracene skeleton.     

Low-Temperature 13C-NMR Spectra of 6Li- and 13C-Labelled Sulfur- and Selenium-Substituted Organolithium Derivatives

The ¹³C-NMR spectra of 19 different, singly, doubly, and triple ¹³C-labelled α-sulfur- and α-selenium-substituted ⁶Li-derivatives generated from methyl and phenyl thioethers, thioacetals, trithio-orthoesters and from their selenium analogues have been recorded in ethereal solutions (tetrahydrofuran (THF), 2-methyltetrahydrofuran (MTHF) at temperatures between ?30° and ?110°. The effects of H/Li-exchange upon chemical shifts and coupling constants, as well as the values and multiplicities of Li, ¹³C-coupling are interpreted in vie wof crystal structures of some of the same compounds. In two thirds of the cases studied, the H-decoupled ¹³C-NMR signals observed below ?80° were triplets, proving that the C-atoms are bonded to single ⁶Li-atoms. This is compatible either with monomeric or with dimeric, heteroatom-bridged structures. The direct ¹H, ¹³C- and ¹³C, ¹³C-coupling constants (¹J) decrease, the ¹³C, ⁷⁷Se-coupling constants increase upon lithiation. More striking is that the geminal coupling ¹³C-S-¹³C (²J) is too small to be observed in the non-metalated species, while it ranges from 3.7 to 7.5 Hz in the lithiated derivatives. These observations may be interpreted as resulting from delocalization of electron density from the carbonionic center towards the adjacent heteroatom.     

13C NMR study of N-unsubstituted aziridines: I—steric effects,pseudoconjugation

¹³C chemical shifts for twenty-nine alkyl and phenyl substituted N-unsubstituted aziridines have been measured. Additivity parameters for methyl, phenyl and aziridyl carbons have been derived with the aim of testing the consistency of the assignments made on the basis of chemical shift considerations and off-resonance decoupling information. The observed chemical shifts are discussed in terms of steric and pseudoconjugation effects.     

Bis[2,2′‐(phenyl­phosphinediyl)­dibenzene­thiol­ato‐κ3S,P,S′]germanium(IV)

Two tridentate phosphinethiol­ate ligands, [PhP(C₆H₄S‐2)₂]²⁻, coordinate to the Ge^IV centre in a facial manner yielding the title compound, [Ge(C₁₈H₁₃PS₂)₂], which exhibits a pseudo‐twofold symmetry with the two P‐atom donors in a cis configuration. The Ge centre has a distorted octahedral environment. Two phenyl rings, one from each of the phosphinethiol­ate ligands, are parallel to one another, indicating π–π interactions. The molecules are linked by weak C—H⋯π and C—H⋯S interactions.     

13C-NMR. Spectra of Natural and Semi-synthetic Cannabinoids

The ¹³C-NMR. spectra of one natural and ten semi-synthetic cannabinoids were analyzed in detail. Assignments of the signals are based on their chemical shifts, splitting patterns in ¹H-off-resonance decoupling experiments and comparison with ¹³C-NMR. data of related cannabinoids. With some compounds final assignments were made by selective ¹H-decoupling experiments and incremental calculations.     

Zur Verwendbarkeit von 13C-Substituenteninkrementen bei 1,4-Benzo- und 1,4-Naphthochinonen

About the Availability of ¹³C-NMR Substituent Increments in 1,4-Benzo- and 1,4-Naphthoquinones The ¹³C-NMR spectra of a number of substituted 1,4-benzo- and 1,4-naphthoquinones have been obtained and assigned. Effects of CH₃-, O-alkyl-, Cl-, NH₂- and N₃- substituents have been deduced for the quinoid part of the molecules and used for the calculation of ¹³C-chemical shifts.     

The structure of α-(1,2-dithiole-3-ylidene) ketones and α-(1,2-dithiole-3-ylidene) aldehydes studied by means of n.m.r. spectroscopy

1H and ¹³C n.m.r. studies of a series of twelve 1,2-dithiole-3-ylidene ketones and aldehydes have shown that the geometry of the carbon backbone is the same as found in 1,6,6aλ⁴-trithiapentalenes. No evidence has been found which favours a bicyclic structure for the system. A linear correlation of observed ¹³C chemical shifts with calculated charge densities is found to be valid. The observations are in agreement with a structure which is a hybrid between a true ketonic structure and a true mesoionic structure. By using the difference in the ¹³C chemical shifts of ortho and meta carbon atoms in substituent phenyl groups it is possible to qualify the degree of coplanarity of the phenyl groups with the backbone of the molecule.     

Structure de modèles de polyesters-4—1: Structure et conformation d'oligomères polytétraméthylène téréphtalate par diffraction des rayons X Et RMN haute résolution dans les solides (RAM-DPC)

The structures of polytetramethylene terephthalate (PTMT) and selected model compounds are described for the solid state [X-ray, ¹³C-NMR (magic angle spinning, and cross polarization)] and in solution. Compounds representative of the unstressed (α) crystalline form of PTMT have isotropic chemical shifts different from those of the stressed (β) form. The chemical shifts are interpreted in terms of conformational differences in the tetramethylene segments.     

Complete assignment of NMR data of 22 phenyl‐1H‐pyrazoles' derivatives

Complete assignment of ¹H and ¹³C NMR chemical shifts and J(¹H/¹H and ¹H/¹⁹F) coupling constants for 22 1‐phenyl‐1H‐pyrazoles' derivates were performed using the concerted application of ¹H 1D and ¹H, ¹³C 2D gs‐HSQC and gs‐HMBC experiments. All 1‐phenyl‐1H‐pyrazoles' derivatives were synthesized as described by Finar and co‐workers. The formylated 1‐phenyl‐1H‐pyrazoles' derivatives were performed under Duff's conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

Etude en Résonance Magnétique Nucléaire du Carbone-13 de Quelques Aminopyrazoles. Sur le Problème de la Détermination des Constantes d'Equilibre Tautomère

The ¹³C chemical shifts of 32 pyrazoles were measured in hexadeuterated dimethyl sulphoxide and in hexamethylphosphorotriamide. Substituent effects (methyl and amino groups on the pyrazolic carbons, and methyl, n-butyl and phenyl groups on the nitrogen) were calculated by multilinear regression analysis. The general problem of the ¹³C NMR study of annular tautomerism in azoles is discussed and illustrated by the 3(5)-aminopyrazole case.     

1H- und 13C-NMR.-Spektren von 6-(p-X-Phenyl)fulvenen. Kurzmitteilung

¹H- and ¹³C-NMR.-spectra of 6-(p-X-phenyl)fulvenes The ¹H- and ¹³C-NMR.-spectra of a series of 6-(p-X-phenyl)fulvenes 3 , measured at 9.39 T (93.9 kgauss), have been analyzed. In these compounds, electronic effects due to the substituent X clearly exert changes in chemical shifts as well as in coupling constants in the 5-membered ring. Small changes in bond length are observed by comparison of the vicinal ¹H, ¹H-coupling constants, whereas changes in charge densities linearly influence the chemical shifts of C(5), C(2) and C(3).