Study of proton chemical shifts and couplings with fluorine-19 in 9.alpha.-fluorocortisol. Application of a novel proton-carbon-13 chemical shift correlation technique with homonuclear decoupling

1984 ◽  
Vol 106 (23) ◽  
pp. 7046-7051 ◽  
Author(s):  
Tuck C. Wong ◽  
Venceslav Rutar ◽  
Jin Shan Wang
Keyword(s):  
Chemical Shift ◽  
Chemical Shifts ◽  
Correlation Technique ◽  
Chemical Shift Correlation ◽  
Homonuclear Decoupling ◽  
Proton Chemical Shifts

scholarly journals The T, p-Dependence of the Chemical Shift of the Hydroxyl Protons in Deeply Supercooled Methanol and Water

2000 ◽  
Vol 55 (3-4) ◽  
pp. 473-477 ◽  
Author(s):  
Liuping Chen ◽  
Thomas Gross ◽  
Hans-Dietrich Lüdemann
Keyword(s):  
Hydrogen Bond ◽  
Chemical Shift ◽  
Chemical Shifts ◽  
Bond Formation ◽  
Hydrogen Bond Formation ◽  
Hydroxyl Proton ◽  
Upfield Shift ◽  
State Models ◽  
Hydroxyl Protons ◽  
Proton Chemical Shifts

The hydroxyl proton chemical shifts δ (H-O) of supercooled methanol (Tmin= 149 K) and water have been determined (Tmin= 183 K), and the pressure dependence of these shifts was measured up to 200 MPa. In both compounds the downfield shift of δ (H-O) continues down to the lowest temperatures reached. This result disagrees with the two state models for the hydrogen bond formation in both liquids. The isotherms δ(H2O) show for T< 273 K an upfield shift that becomes more pronounced with decreasing temperature. For δ ( H-O-CH3), increasing p causes at all temperatures a downshift

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.

Proton chemical shifts and electron densities in aromatic and heteroaromatic molecules. I. Procedure and chemical shift corrections; Applications to azines

1967 ◽  
Vol 20 (7) ◽  
pp. 1305 ◽  
Author(s):  
PJ Black ◽  
RD Brown ◽  
ML Heffernan
Keyword(s):  
Chemical Shift ◽  
Electric Field ◽  
Electron Distribution ◽  
Theoretical Calculations ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Excess Charge ◽  
Heteroaromatic Compounds ◽  
Electric Field Dependence ◽  
Proton Chemical Shifts

In this series, the observed proton chemical shifts of heteroaromatic compounds are used to obtain estimates of the electron distribution in these systems. These estimates are deduced from the measured shifts after applying corrections for the shielding contributions arising from ring currents, magnetic anisotropy of neighbouring atoms, and the electric field from the lone-pair dipoles on heteroatoms, in a manner closely related to that of Gil and Murrell. The corrected chemical shifts are then used to deduce an ?experimental? π-electron distribution via the electric field dependence of the proton shifts on the excess charge at all ring positions. However, in most cases, there are not enough experimental shifts to determine uniquely the excess charge at each ring atom, and it is necessary to assume that some inaccessible charges are close to values obtained from theoretical calculations. With these limitations, a comparison is made between the excess charges deduced in the above fashion from chemical shift data on mono- and poly-cyclic azines and diazines and those obtained by theoretical calculations using the BJ VESCF method. It is emphasized that this interpretation is tentative and that the extent of σ-electron polarization is not well understood at present.

Experimental chemical shift correlation maps from heteronuclear two-dimensional nuclear magnetic resonance spectroscopy. II: Carbon-13 and proton chemical shifts of a-D-glucopyranose oligomers

1982 ◽  
Vol 60 (19) ◽  
pp. 2431-2441 ◽  
Author(s):  
Gareth A. Morris ◽  
Laurance D. Hall
Keyword(s):  
Chemical Shifts ◽  
2D Nmr ◽  
Resonance Spectroscopy ◽  
Two Dimensional ◽  
Chemical Shift Correlation ◽  
Proton Pair ◽  
Double Fourier Transform ◽  
Nmr Methods ◽  
Proton Chemical Shifts ◽  
Experimental Chemical Shift

Double Fourier transform ("2D") nmr methods allow the simultaneous measurement of proton and carbon-13 chemical shifts for each directly bonded carbon–proton pair in a molecule. As well as greatly increasing the number of different resonances that may be distinguished in the spectra of complex systems, the measurement of correlated proton and carbon-13 shifts allows the otherwise inaccessible proton shifts to be determined, and facilitates the assignment of conventional proton and carbon-13 spectra. Results are presented for glucose, maltose, maltotriose, α-cyclodextrin, β-cyclodextrin, and dextran T-10; reassignments are proposed for the carbon-13 spectra of maltose and maltotriose.

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