scholarly journals Bridge effect of the C=C, C=N and N=N bonds on the long distance electronic charge transfer ofpara‒substituted stilbenoid compounds

2000 ◽  
Vol 14 (4) ◽  
pp. 259-267 ◽  
Author(s):  
Manuel A. Leiva ◽  
Raul G. E. Morales
Keyword(s):  
Charge Transfer ◽  
Double Bond ◽  
Molecular System ◽  
Chemical Shifts ◽  
Phenyl Group ◽  
Point Of View ◽  
Electronic Charge ◽  
Orbital Theory ◽  
Long Distance ◽  
C Nmr

By means of13C‒NMR spectroscopy and ab initio molecular orbital theory calculations, we have analyzed the bridge effect of the C=C, C=N and N=N bonds on the long distance charge transfer of4‒dimethylamino‒4'‒nitrostilbenoid compounds in the ground electronic state.After a complete spectral assignment of the13C‒NMR signals in these molecular compounds, we have characterized the effect of the nitrogen centres on the molecular bridge by means of the chemical shifts of the carbon centres, the theoretical charge densities and the dipolar moments.From an electronic molecular point of view, our results describe two main properties of the double bond bridge. The first is related to the local charge accumulation capacity given by the type of the atomic centres and the structural orientation of the double bond bridge, and the second property is related to the modulation of the electronic charge distribution through the molecular system by the electrical polarization of the bridge.Other complementary experimental evidences have permit us to establish new local molecular domains of the bridge effect in these stilbenoid compounds by means of linear correlations between13C‒NMR chemical shifts of the aromatic carbon centres of the acceptor‒phenyl group and the molecular polarity of the species under study.

scholarly journals HR-DOSY and sulfoxide enantiomeric discrimination by cyclodextrin

2000 ◽  
Vol 14 (4) ◽  
pp. 203-213 ◽  
Author(s):  
Ricardo Batista Borges ◽  
Antonio Laverde Jr. ◽  
André Luiz Meleiro Porto ◽  
Anita Jocelyne Marsaioli
Keyword(s):  
Chiral Recognition ◽  
Chemical Shifts ◽  
Binding Constants ◽  
Chiral Selector ◽  
Point Of View ◽  
The Other ◽  
Stoichiometric Ratio ◽  
Enantiomeric Resolution ◽  
Rp Hplc ◽  
C Nmr

Racemic and chiral ethyl-phenylsulfoxide (solute) andβ-cyclodextrin (chiral selector) were used to compare two NMR methodologies to predict RP-HPLC enantiomeric resolution efficiency. One of them based on the classical approach involving apparent binding constants and complexation‒induced chemical shifts at saturation and the other based on13C NMR signal splittings (solute and chiral selector in stoichiometric ratio) and HR-DOSY of the same solution. We have concluded that the latter methodology is rather efficient and though more elaborate from the NMR point of view, the results are promising and constitute an alternative method to investigate chiral recognition and other supramolecular phenomena.

Characterization and spectroelectrochemical properties of a binuclear trans,trans-bis(ferrocenylidene)acetone [(C5H5)Fe(C5H4CHCH)]2CO

1990 ◽  
Vol 68 (2) ◽  
pp. 223-227 ◽  
Author(s):  
Pierre D. Harvey ◽  
Jeff G. Sharman
Keyword(s):  
Charge Transfer ◽  
Excited States ◽  
Emission Spectroscopy ◽  
Electronic Charge ◽  
Oxidative Process ◽  
Ft Ir ◽  
Triplet Excited States ◽  
Electronic Charge Transfer ◽  
Spectroelectrochemical Properties ◽  
C Nmr

The binuclear compound trans,trans-bis(ferrocenylidene)acetone [(C5H5)Fe(C5H4CHCH)]2CO (dFca) has been synthesized in quantitative yield and characterized by FT-IR, 1H and 13C NMR, and mass spectroscopy. Cyclic voltammetry and coulometry measurements suggest that a reversible two-electron oxidative process takes place at 0.68 V vs. SSCE. FT-IR and UV–VIS spectroelectrochemical analyses show that this oxidative process occurs at the ferrocenyl centers. The compound is also found to be emissive in the solid state (λmax = 780 nm), and charge transfer assignments for the lowest singlet and triplet excited states are made. Keywords: ferrocenyl, spectroelectrochemistry, electronic charge transfer, emission spectroscopy.

Carbon-13 nuclear magnetic resonance spectral study of some isomeric derivatives of 2-methoxytropone. Troponoid-II

1979 ◽  
Vol 57 (15) ◽  
pp. 1949-1957 ◽  
Author(s):  
J. F. Bagli ◽  
T. Bogri ◽  
B. Palameta ◽  
M. St-Jacques
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Charge Transfer ◽  
Magnetic Resonance ◽  
Spectral Study ◽  
Nmr Spectra ◽  
Membered Ring ◽  
Electronic Charge ◽  
Derivatives Of ◽  
Electronic Charge Transfer ◽  
C Nmr

The 13C nmr spectra of several isomeric monosubstituted derivatives of 2-methoxytropone together with some dibromo derivatives have been obtained and analysed. Substituent parameters were defined and shown to exhibit additivity. Differences with corresponding parameters for monosubstituted benzene analogs suggest proximity interactions between the 3-substituents and the 2-OCH3 group as well as between 7-substituents and the adjacent carbonyl group. The data indicates that the OCH3 group is a convenient probe to investigate the orientation of mesomeric electronic charge transfer to the various carbons of the tropone seven-membered ring. Finally, it is demonstrated that 13C nmr is quite useful to distinguish between the various substituted 2-methoxytropones.

13C NMR spectroscopy of heterocycles: 1-phenyl-3-aryl/t-butyl-5-arylpyrazoles

2017 ◽  
Vol 23 (2) ◽  
pp. 125-131 ◽  
Author(s):  
Amy N. Hockstedler ◽  
Beatrice A. Edjah ◽  
Saajid Z. Azhar ◽  
Hadrian Mendoza ◽  
Nicole A. Brown ◽  
...  
Keyword(s):  
Chemical Shifts ◽  
Substituent Effects ◽  
Phenyl Group ◽  
13C Nmr Spectroscopy ◽  
Aryl Group ◽  
Torsion Angles ◽  
Chemical Shift Data ◽  
Molecular Modeling Studies ◽  
Shift Data ◽  
C Nmr

AbstractA series of chalcones 1–12 were converted to pyrazolines (1Pi–12Pi) by reaction with phenylhydrazine followed by DDQ oxidation to produce the corresponding pyrazoles (1Pz–12Pz). Three 1-phenyl-3-t-butyl-5-arylpyrazoles (13Pz–15Pz) were synthesized using an analogous approach. Molecular modeling studies predicted the 5-aryl group of the pyrazoles for both series to have a torsion angle of 52°–54° whereas the 1-phenyl group was predicted to have 35°–37° torsion angles. The 3-aryl group was predicted to be essentially coplanar (−3°) with the pyrazole system in the first series. 13C NMR data for both series, 1Pz–12Pz and 13Pz–15Pz, were collected in DMSO-d6 at 50°C. A plot of the C4 chemical shifts for 1Pz–12Pz versus Hammet constants for 5-aryl substituents yielded a very good linear correlation (R2=0.96) with a slope of 1.5. The chemical shift data for C4 showed little or no dependence on 3-aryl substituents. The result for 13Pz–15Pz, despite only three points, was consistent with the first series results and yielded a ρ value of 2.0. Distal transmission of substituent effects (5-aryl groups) to C4 of the pyrazole system was reduced by roughly 50–60% of that of the analogous planar isoxazole system, but are not consistent with results for the similarly twisted 4-bromoisoxazoles.

Some Considerations Regarding the 1H and 13C Spectra of 4-(1-azulenyl)-2,6-bis(2-heteroaryl-vinyl)- pyrylium and Pyridinium and their Corresponding Pyridines

2018 ◽  
Vol 69 (1) ◽  
pp. 64-69
Author(s):  
Liviu Birzan ◽  
Mihaela Cristea ◽  
Constantin C. Draghici ◽  
Alexandru C. Razus
Keyword(s):  
Double Bond ◽  
13C Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Pyridinium Salts ◽  
13C Nmr Spectra ◽  
1H And 13C Nmr ◽  
Pyrylium Salts

The 1H and 13C NMR spectra of several 2,6-diheteroarylvinyl heterocycles containing 4-azulenyl moiety were recorded and their proton and carbon chemical shifts were compared with those of the compounds without double bond between the heterocycles. The influence of the nature of central and side heterocycles, molecule polarization and anisotropic effects were revealed. The highest chemical shifts were recorded for the pyrylium salts and the lowest at pyridines, but in the case of the pyridinium salts, the protons chemical shifts at the central heterocycle are more shielded due to a peculiar anisotropy of the attached vinyl groups.

17O and 13C NMR spectra of some geminal diacetates

1988 ◽  
Vol 53 (3) ◽  
pp. 588-592 ◽  
Author(s):  
Antonín Lyčka ◽  
Josef Jirman ◽  
Jaroslav Holeček
Keyword(s):  
13C Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
The Other ◽  
13C Nmr Spectra ◽  
Other Hand ◽  
Carboxylic Esters ◽  
C Nmr ◽  
Oxygen Atoms

The 17O and 13C NMR spectra of eight geminal diacetates RCH(O(CO)CH3)2 derived from simple aldehydes have been measured. In contrast to the dicarboxylates R1R2E(O(CO)R3)2, where E = Si, Ge, or Sn, whose 17O NMR spectra only contain a single signal, and, on the other hand, in accordance with organic carboxylic esters, the 17O NMR spectra of the compound group studied always exhibit two well-resolved signals with the chemical shifts δ(17O) in the regions of 183-219 ppm and 369-381 ppm for the oxygen atoms in the groups C-O and C=O, respectively.

Carbon-13 and nitrogen-14 NMR spectra of 1-(substituted phenyl)pyridinium salts

1980 ◽  
Vol 45 (10) ◽  
pp. 2766-2771 ◽  
Author(s):  
Antonín Lyčka
Keyword(s):  
Heavy Water ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Pyridinium Salts ◽  
Nmr Signals ◽  
C Nmr

The 13C and 14N NMR spectra of 1M solutions of 1-(substituted phenyl)pyridinium salts (4-CH3, 4-OCH3, H, 4-Cl, 4-Br, 4-I, 3-NO2, 4-NO2, 2,4-(NO2)2 (the 13C NMR only)) have been measured in heavy water at 30 °C. The 13C and 14N chemical shifts, the 1J(CH) coupling constants, some 3J(CH) coupling constants, and values of half-widths Δ 1/2 of the 14N NMR signals are given. The 13C chemical shifts of C(4) correlate with the σ0 constants (δC(4) = (1.79 ± 0.097) σ0 + (147.67 ± 0.041)), whereas no correlation of the nitrogen chemical shifts with the σ constants has been found. The half-widths Δ 1/2 correlate with the σ0 constants (Δ 1/2 = (76.2 ± 4.9) σ0 + (106.4 ± 2.2)) except for 1-phenylpyridinium chloride.

Gradient-Enhanced Inverse-Detected NMR Techniquesfor Determination of 1H-15N Coupling Constants in 2,2-Dimethylpenta-3,4-dienal Derivatives

1997 ◽  
Vol 62 (11) ◽  
pp. 1747-1753 ◽  
Author(s):  
Radek Marek
Keyword(s):  
Double Bond ◽  
Chemical Shifts ◽  
Multiple Bond ◽  
Coupling Constants ◽  
Single Quantum ◽  
Nmr Techniques ◽  
Phase Sensitive ◽  
Heteronuclear Coupling

Determination of 15N chemical shifts and heteronuclear coupling constants of substituted 2,2-dimethylpenta-3,4-dienal hydrazones is presented. The chemical shifts were determined by gradient-enhanced inverse-detected NMR techniques and 1H-15N coupling constants were extracted from phase-sensitive gradient-enhanced single-quantum multiple bond correlation experiments. Stereospecific behaviour of the coupling constants 2J(1H,15N) and 1J(1H,13C) has been used to determine the configuration on a C=N double bond. The above-mentioned compounds exist predominantly as E isomers in deuteriochloroform.

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