Chemical Shift. VI. The Long-range Shielding Effects of Ethylene–Ketal and −Thioketal Groups

1971 ◽  
Vol 49 (9) ◽  
pp. 1335-1338 ◽  
Author(s):  
J. W. ApSimon ◽  
H. Beierbeck ◽  
D. K. Todd ◽  
P. V. Demarco ◽  
W. G. Craig
Keyword(s):  
Chemical Shift ◽  
Electric Field ◽  
Long Range ◽  
Field Effect ◽  
Chemical Shifts ◽  
Electric Field Effect ◽  
Electric Dipoles ◽  
Derivatives Of ◽  
Shielding Effects

The calculation of chemical shift values by the method used in parts I–V (1–5) has been extended to a derivation of the shielding effects of the ethylene–ketal and −thioketal groups. For these studies ketal and thioketal derivatives of monoketoandrostanes were prepared. The chemical shifts of the C-18 and -19 methyl protons in these compounds are reported for the solvents CDCl3, CCl4 and benzene.Representing both groups by point dipoles, values for the anisotropies and for K, a parameter descriptive of the electric field effect, were derived for various, coincidental, locations of the magnetic and electric dipoles along the symmetry axes of the two groups.

Chemical Shift. VII. The Long-range Shielding Effects of the Cyano Group

1972 ◽  
Vol 50 (14) ◽  
pp. 2351-2356 ◽  
Author(s):  
J. W. ApSimon ◽  
H. Beierbeck ◽  
D. K. Todd
Keyword(s):  
Chemical Shift ◽  
Long Range ◽  
Field Effect ◽  
Cyano Group ◽  
Electric Field Effect ◽  
Minor Contribution ◽  
Anisotropy Effect ◽  
A Minor ◽  
Good Agreement ◽  
Shielding Effects

Using the methods described in parts I–VI of this series, we have examined the long-range shielding effects of the cyano group upon the C-18 and -19 methyl protons in several cyano-steroids and the ring protons in 2-endo- and 2-exo-cyanonorbornenes.It was found that the most important shielding mechanism of the cyano group is its electric field effect, with the magnetic anisotropy effect making at most a minor contribution to the screening. However, only in the cases of the cyano-steroids was good agreement obtained between the calculated and the experimental shifts.

Evidence for the existence of an electric field effect from the vinyl proton magnetic resonance spectra of 4-substituted styrenes

1968 ◽  
Vol 46 (24) ◽  
pp. 3813-3820 ◽  
Author(s):  
G. K. Hamer ◽  
W. F. Reynolds
Keyword(s):  
Chemical Shift ◽  
Electric Field ◽  
Field Effect ◽  
Chemical Shifts ◽  
Electric Field Effect ◽  
Vinyl Proton ◽  
Concentration Effects ◽  
Electric Field Effects ◽  
Field Effects ◽  
Proton Chemical Shifts

Vinyl proton chemical shifts of styrene and six 4-substituted styrenes have been determined at infinite dilution in cyclohexane. It is shown that changes in the chemical shift difference of the β protons, Δ(δC − δB) can be accounted for by electric field effects. Reasonable values of the constant in the Buckingham equation of(−3.11 ± 0.50) × 10−12 and (−4.77 ± 0.83) × 10−12 are obtained from two different types of field effect calculations. Residual chemical shift changes for β protons after correction for electric field effects can be explained in terms of mesomeric and possibly inductive mechanisms. α-Proton chemical shift values cannot be satisfactorily rationalized. Small concentration effects are noted, usually resulting in high field shifts with increasing concentration. Previous results are reexamined in order to resolve a conflict in the literature.

1.3-Dithienium-and 1.3-Dithiolenium Salts, VI ,13C NMR Spectroscopic Investigations on 2-Substituted 1,3-Dithian-2-ylium Cations. Unusual γ-Effects

1997 ◽  
Vol 52 (6) ◽  
pp. 757-761 ◽  
Author(s):  
Hans-Otto Kalinowski ◽  
Ingfried Stahl
Keyword(s):  
Electric Field ◽  
Density Distribution ◽  
13C Nmr ◽  
Field Effect ◽  
Electron Density Distribution ◽  
Chemical Shifts ◽  
Membered Ring ◽  
Electric Field Effect ◽  
Polarisation Effect ◽  
C Nmr

Abstract The 13C NMR chemical shifts of 19 2-substituted 1,3-dithian-2-ylium-tetrafluorborates 1a-1s are discussed in comparison to known analogous 1,3-dithianes and 2-lithio-1,3-dithianes. The unusual γ-effects (up to 9 ppm), which can also observed in other six-membered ring systems, are explained by the electric field effect (σ-polarisation effect). The electron density distribution can be estimated qualitatively by comparison with the 1,3-dioxan-2-ylium-and cyclohexylcations.

SUBSTITUTIONAL AND CONFIGURATIONAL EFFECTS ON CHEMICAL SHIFT IN PYRANOID CARBOHYDRATE DERIVATIVES

1965 ◽  
Vol 43 (7) ◽  
pp. 2059-2070 ◽  
Author(s):  
R. U. Lemieux ◽  
J. D. Stevens
Keyword(s):  
Chemical Shift ◽  
Long Range ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Equatorial Orientation ◽  
Free Energies ◽  
Bonding Interaction ◽  
Conformational Properties ◽  
Good Agreement ◽  
Shielding Effects

The effects of long-range and virtual long-range coupling on the observed spectra of acetylated hexopyranoses and pentopyranoses are examined. Use is made of both spin decoupling and specific deuteration for the assignment of signals. It is seen that specific solvent effects on chemical shift can be superior to increasing the applied magnetic field for the resolution of the signals of closely related protons. The alteration of virtual long-range coupling effects in these ways can be useful in the diagnosis of spectra. Empirical rules are derived for estimating the long-range shielding effects which occur on changing configurations. It is seen that the inversion of a center can lead to deshielding of axial protons and to shielding of equatorial protons at other centers relative to the chemical shifts observed in reference compounds wherein all the acetoxy groups are in equatorial orientation. The effects in several cases result in equatorial protons giving their signal to higher field than chemically similar but axial protons. The conformational properties of pentopyranose tetraacetates as estimated from chemical shifts and coupling constants are seen to be in good agreement with expectations based on non-bonding interaction free energies. As expected, 2-deoxy-β-D-ribopyranose triacetate has the 1C-conformation when dissolved in chloroform.

Long-Range Nonvolatile Electric Field Effect in Epitaxial Fe/Pb(Mg1/3 Nb2/3 )0.7 Ti0.3 O3 Heterostructures

2018 ◽  
Vol 28 (20) ◽  
pp. 1707027 ◽  
Author(s):  
Cai Zhou ◽  
Lvkang Shen ◽  
Ming Liu ◽  
Cunxu Gao ◽  
Chenglong Jia ◽  
...  
Keyword(s):  
Electric Field ◽  
Long Range ◽  
Field Effect ◽  
Electric Field Effect

scholarly journals Long-range spin–spin coupling in N-methyl 2-carbomethoxy-4,6-dinitroaniline

1970 ◽  
Vol 48 (6) ◽  
pp. 934-941 ◽  
Author(s):  
J. A. McCubbin ◽  
R. Y. Moir ◽  
G. A. Neville
Keyword(s):  
Magnetic Resonance ◽  
Carbonyl Group ◽  
Long Range ◽  
Proton Magnetic Resonance ◽  
Chemical Shifts ◽  
Relative Magnitude ◽  
Spin Coupling ◽  
Spin Spin Coupling ◽  
Derivatives Of ◽  
Shielding Effects

Long-range coupling [Formula: see text] between the amino proton and the C-5 ring proton of N-methyl 2-carbomethoxy-4,6-dinitroaniline (1) was established unequivocally by comparison of the proton magnetic resonance spectra of the 3-d and 5-d analogs of 1 together with the N-deutero derivatives of the above compounds. Deuterium decoupling experiments indicated that meta-deuterium coupling was of the order of band resolution (< 0.2 Hz). Elucidation of the source of long-range coupling with the amino proton enabled the chemical shifts of the aromatic protons to be assigned. The relative magnitude of these chemical shifts is discussed in terms of the shielding effects operative in the predominant conformer in which the amino hydrogen is intramolecularly hydrogen bonded to the oxygen of the ester carbonyl group.

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