Study of electron spin crossover in iron(III) tris-dithiocarbamate complexes by carbon-13 NMR spectroscopy

¹³C and ¹H isotropic shifts have been measured for a series of Fe(III) tris-dithiocarbamate complexes. The ¹³C isotropic shifts may be interpreted as arising solely from contact hyperfine coupling and demonstrate that as the low-spin state of the metal is favoured there is an increase in metal-ligand π-bonding. σ-delocalization of unpaired spin density is more important in determining the ¹³C isotropic shifts than those of the contiguous proton.     

NMR study of the spatial structure of synthetic pyrethroids

The spatial isomers of the new synthetic analogs of ethyl permithrinic ether and permethrin were investigated by NMR (¹H, ¹³C, DEPT (distortionless enhancement by polarization transfer), COSY (correlation spectroscopy), CHCORR (heteronuclear (C, H) shift correlation spectroscopy), ROESY (rotating-frame Overhauser effect spectroscopy)). Several tendencies were revealed in the ¹H and ¹³C chemical shifts of the α atoms of the substituents in the 2nd and 3rd positions of the cyclopropane ring. For substituents cis-orientated relative to the ester group, the spectra show a paramagnetic shift of the ¹H signals and the diamagnetic shift of the ¹³C signals relative to the trans-orientated substituents. The ¹H and ¹³C chemical shifts of the α atoms of the substituents in the 2nd and 3rd positions of the cyclopropane ring permit an unambiguous determination of the stereochemistry of ethyl permethrinic ether and permethrin analogs.     

NMR spectroscopic study of 3-nitrofurazans

3-Nitrofurazans with different substituents at position 4 were studied by ¹H, ¹³C, and ¹⁴N NMR spectroscopy. A correlation between chemical shifts (CS) in the ¹³C NMR spectra of furazans and benzene with similar substituents was revealed. Increments for a series of new substituents were determined. The ¹³C and ¹⁴N CS values presented can be used as a reliable set of reference data.     

Electronic effects in the cyclopentadienyl ring. The 13C NMR spectraof monosubstituted ferrocenes

The chemical shifts of C(2,5) and C(3,4) carbons in the ¹³C NMR spectra of monosubstituted ferrocenes have been assigned using deuterium labelling. An analogy is observed between the shielding of C(2,5) and C(3,4) carbons of ferrocene derivatives and ortho- and para-carbons of benzene derivatives withthe same substituents. Electron-density distribution in the cyclopentadienyl ring is discussed on the basis of ¹³C NMR data.     

Carbon-13 NMR studies of some paramagnetic transition-metal acetylacetonates some linewidth considerations

Carbon 13 isotropic shifts and linewidths have been measured for a series of paramagnetic transition-metal acetylacetonates. The results have been compared with the corresponding NMR parameters of the contiguous protons. The relaxation pathway of the ¹³C spins is controlled by hyperfine interactions with the unpaired electron spins and, in cases where the proton linewidth is also dominated by the hyperfine mechanism, good agreement is obtained between the experimental ¹³C/¹H linewidth ratio and that calculated on the basis of the contact shifts. Pseudocontact interactions can be important in determining the total isotropic shift for both the ¹³C and ¹H nuclei and contrary to previous studies, it is suggested that such effects are also important for V(III) and Mn(III) acetylacetonate.     

1H, 13C,and 14N NMR study of 3-methylfurazans with nitrogen-containing substituents at position 4

3-Methylfurazans with nitrogen-containing substituents at position 4 were studied by ¹H, ¹³C, and ¹⁴N NMR spectroscopy. A correlation between the chemical shifts in ¹³C NMR spectra of these furazans and monosubstituted benzenes with the same substituents was found. The increments for a number of furazan-containing substituents were determined for the first time.     

RMN 13C de cyclanones halogénées. Détermination et additivité des incréments du chlore en série cyclohexanique

The ¹³C n.m.r. spectra of fourteen chlorocyclohexanones have been recorded to examine the variation of the ¹³C chemical shifts as a function of the position and the number of the chlorine substituents. Additivity relationships were found which enable reasonable prediction of the chemical shifts of chlorinated cyclohexanones. Comparison between the observed and calculated chemical shifts of mono- and dichlorinated flexible molecules shows that the chlorine effects are additive.     

Carbon-13 NMR investigation of 2,5-diaryl-1,4-dithiins

The ¹³C NMR spectra of eight 2,5-diaryl-1,4-dithiins were recorded and signals were assigned. A linear correlation was observed between the electronegativity of the substituent groups on C-10,10′ and the chemical shifts of C-10,10′ after applying corrections for the magnetic anisotropic effect of the substituents. A Hammett correlation was found between the ¹³C chemical shifts of C-3,6 and C-7,7′ and the σ_p⁺ parameter associated with the substituents on C-10,10′. Extended electronic interaction between the π system of the aryl group and the π system of the dithiin ring was suggested by the observance of an alternating behavior in the magnitude of the substituent effects on the ¹³C shifts of C-2,5 and C-3,6. An alternating effect was also noted in the magnitude of the long-range ¹³C? F coupling constants for these same carbon signals in 2,5-(10,10′-difluoro)diphenyl-1,4-dithiin.     

NMR-Untersuchungen an Dicyclopentadienderivaten. IV—1-Syn/anti-Epimere von endo-Dicyclopentadienderivaten

The syn/anti-arrangement of some substituents R in position 1 of endo-dicyclopentadiene derivatives is investigated by ¹H-and ¹³C n.m.r. spectroscopy. The HH-coupling constants of the epimeric alcohols 2 and 3 are determined by paramagnetic shift experiments [Eu(fod)₃] and the observed relative paramagnetic shifts ΔEu used for the determination of the configuration. The increasing steric compression in the syn-epimers is well reflected by the ¹H- and ¹³C n.m.r. chemical shifts.     

Carbon-13 n.m.r. spectra of branched carboxylic acids and their derivatives

¹³C n.m.r. spectra have been measured for 39 compounds with branched structures including carboxylic acids, their methyl and ethyl esters, nitriles and chlorinated esters. The results obtained indicate that the ¹³ C n.m.r. technique is applicable to structure assignment of acids and their derivatives containing various numbers of substituents on the chain. The dependence of the carboxylic carbon chemical shift on the number and structure of α-positioned substituents has been determined. Calculation of the chemical shifts for branched carboxylic acids, esters and nitriles from the corresponding increments using the additivity scheme is shown to be possible in principle.     

13C and 1H chemical shifts in 2-benzylidene[3]ferrocenophane-1,3-diones. Elucidation of the substituent dependence of carbonyl chemical shifts in different carbonyl derivatives

The ¹³C and ¹H chemical shifts of the ferrocene moiety, as well as the carbonyl carbons and styrene moiety, of substituted 2-benzylidene[3]ferrocenophane-1,3-diones have been assigned. Correlations of ¹³C substituent chemical shifts of both carbonyl carbons with the Hammett constants have been found, and the effect of the transmission of substituent effects on these chemical shifts through the styrene moiety is discussed. An explanation is given for the different sensitivities of the carbonyl carbon chemical shifts to the electronic effect of substituents in mono- and dicarbonyl derivatives.     

Carbon-13 magnetic resonance studies of cyclic compounds. 2. Carbon-13 chemical shift parameters for equatorial and axial substituents in cyclohexane: The substituents methyl,ethyl, isopropyl,methoxy and phthalimido

Carbon-13 chemical shift parameters for equatorial and axial substituents in cyclohexane are reported for methyl, ethyl, isopropyl, methoxy and phthalimido substituents. The usefulness of the alkyl parameters is demonstrated by the agreement between calculated and observed ¹³C shifts for trans-1,4-dialkylcyclohexanes (alkyl = Me, Et, i-Pr) and for both conformations of cis-1,4-dialkylcyclohexanes (alkyl = Me, Et, i-Pr).     

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.     

13C NMR spectra of 1-(N-arylidene)amino-1,2,3-triazoles

The ¹³C nmr spectra of several 1-(N-arylidene)amino-1,2,3-triazoles were determined. The long range influence of substituents on ¹³C resonances of triazole and C = N carbon atoms was examined and a correlation of their chemical shifts with net charge densities (q_{π + σ}) calculated by the CNDO/2 method was made. It was also shown that the dependence of the coupling constants ¹J(CH) for C = N carbon on the substituents is better correlated using electrons in bond values instead of charge densities.     

Etude en Résonance Magnétique Nucléaire du Carbone-13 de N-Aryl Pyrazolines-2 Diversement Substituées. Effets de Substituant et Etude Conformationnelle

The ¹³C chemical shifts of 1-phenyl-2-pyrazoline and 25 N-nitrophenyl-2-pyrazolines, with different substituents on the heterocyclic ring, have been assigned. These values are discussed as a function of the steric and electronic nature of the various substituents. The steric effects produced conformational modifications, both in the nitrophenyl and 2-pyrazoline moieties, which explain some of the chemical shifts.     

13C and proton NMR spectra of 2(1H)pyrazinones

¹³C and proton NMR spectra data are given for eleven 2(1H)pyraziones. Assignments of chemical shifts were made by methods which included: deuterium exchange with certain protons of 3-alkyl substituents; change of chemical shifts of certain carbon atoms with change in pH; the use of long-range coupling constants for ¹³C to protons; and various correlations among assigned spectra.     

17O, 13C and 1H NMR and IR spectral study of crowded ketones: possible intramolecular C—H···O interactions

Unusual behaviour was observed in the study of the ¹⁷O, ¹³C and ¹H NMR and IR spectra of crowded (1‐adamantyl)alkyl ketones. As the size of the alkyl substituent is increased, abnormal upfield chemical shifts in the ¹³C NMR and downfield shifts in the ¹⁷O NMR of the carbonyl group, as well as downfield shifts in the ¹H NMR of the adamantyl γ'‐protons, are found. In the IR spectrum, the ν_C?O stretching frequencies of the ketones with bulky substituents show considerable red shifts. Correlation of the NMR shifts with the number of γ‐carbon atoms of the alkyl substituents and comparison with the IR results indicated that there is an intramolecular through‐space CH···O interaction in crowded ketones. This was supported by the results of ab initio calculations. Copyright © 2002 John Wiley & Sons, Ltd.     

Carbon-13 NMR studies of substituted naphthalenes. I—complete assignments of the 13C chemical shifts with the aid of deuterated derivatives

Proton-coupled as well as noise-decoupled ¹³C NMR spectra of several substituted naphthalenes have been studied. Complete assignments of the ¹³C signals based on selectively deuterated derivatives and on the ¹³C? ¹H coupling pattern have been made. For the methoxynaphthalenes, acetylnaphthalenes and naphthaldehydes the dominant conformations of the substituents have been deduced from the ¹³C chemical shifts.     

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.     

Etudes des sélénophènes mono et bisubstitués par Résonance Magnétique de 1H et de 13C

Proton and carbon magnetic resonance spectra of mono-and disubstituted selenophenes are investigated. The proton chemical shifts are discussed in terms of magnetic anisotropy and electric field effects of the substituents, with a view to studying the conformational equilibrium of the carbonyl group. π Electronic charges, computed by the PPP method, are correlated with the proton and carbon chemical shifts. The coupling constants between ¹³C and ¹H (1, 2 or 3 bonds) and ¹³C? ⁷⁷Se are shown to be good structural parameters and a set of substituent additivity constants is calculated.