Nuclear Magnetic Resonance Studies of Multi-site Chemical Exchange. II. Hindered Rotation in N,N-Dimethyl Carbamyl Fluoride

1971 ◽  
Vol 49 (22) ◽  
pp. 3671-3682 ◽  
Author(s):  
L. W. Reeves ◽  
K. N. Shaw
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Exchange ◽  
Chemical Shifts ◽  
Activation Parameters ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Matrix Formulation ◽  
Hindered Rotation ◽  
Nuclear Magnetic

The matrix formulation of the Bloch equations including chemical exchange reported earlier is extended to include indirect spin–spin coupling in first-order spectra. The ABX (JAB = 0) spin system is treated in detail and particular attention is paid to the determining effect on the nuclear magnetic resonance (n.m.r.) lineshapes of the relative signs of the coupling constants JAX and JBX. The hindered rotation for N,N-dimethyl carbamyl fluoride in CCl4 as solvent has been studied using a complete 1H n.m.r. lineshape analysis and the activation parameters obtained are: ΔG≠ = 18.1 ± 0.6 kcal mol−1, ΔH≠ = 17.7 ± 0.6 kcal mol−1, and ΔS≠ = −1.4 ± 2.1 cal deg−1 mol−1 at 25 °C.The complete lineshape fits give very precise values of the relative shifts (16.5 mol% in CCl4) of the methyl groups and of the coupling constants JAX (0.30 ± 0.05 Hz) and JBX (0.80 ± 0.05 Hz) at all temperatures. A 40% change in JBX (1.10 ± 0.05 Hz) is observed in neat DMCF from a lineshape fit at −15 °C. The origin of changes in chemical shifts with temperature and JBX with solvent is discussed.

Nuclear Magnetic Resonance Studies of Multi-site Chemical Exchange. III. Hindered Rotation in Dimethylacetamide, Dimethyl Trifluoro-acetamide, and Dimethyl Benzamide

1971 ◽  
Vol 49 (22) ◽  
pp. 3683-3691 ◽  
Author(s):  
L. W. Reeves ◽  
R. C. Shaddick ◽  
K. N. Shaw
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Exchange ◽  
Chemical Shifts ◽  
Activation Parameters ◽  
Type Systems ◽  
Hindered Rotation ◽  
Fitting Procedure ◽  
Nuclear Magnetic

The experimental application of a multi-site exchange theory developed recently has been made to three restricted rotation barriers in amido-type systems. Inclusion of 8 spin-sites in the analyses of the line shapes for spectra of N,N-dimethyl trifluoroacetamide and dimethyl acetamide leads to improved values for the activation parameters. Variation of chemical shifts with temperature is included in the iterative fitting procedure. The determination of the relative signs of long range couplings and the inclusion and measurement of unresolved couplings has been accomplished. The barrier for hindered rotation in N,N-dimethyl benzamide has been re-investigated including the effect of relatively large chemical shift changes with temperature. The internal consistency of the measurements from all aspects indicates that systematic errors common in the determination of energy barriers by steady-state nuclear magnetic resonance (n.m.r.) have been largely eliminated and hence the activation parameters obtained form a reliable addition to a compilation of experimental data pertaining to the bonding in a related series of simple C-substituted amides.

PREFERRED RESIDENCE CONFORMATIONS OF DIASTEREOISOMERIC α–β AMINO ALCOHOLS: AN N.M.R. STUDY OF THE EPHEDRINES

1961 ◽  
Vol 39 (12) ◽  
pp. 2536-2542 ◽  
Author(s):  
J. B. Hyne
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Hydrogen Bonding ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Amino Alcohols ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Nuclear Magnetic

Nuclear magnetic resonance spectral results including chemical shifts, anisotropy effects, spin coupling constants, and hydrogen bonding phenomena are presented for the diastereoisomeric pair of α–β amino alcohols (−)-ephedrine and (+)-Ψ-ephedrine. The results are shown to be in keeping with the existence of a preferred residence conformation for each of the diastereoisomers.

13C nuclear magnetic resonance spectra of 3,6-disubstituted pyridazines

1991 ◽  
Vol 69 (6) ◽  
pp. 972-977 ◽  
Author(s):  
Gottfried Heinisch ◽  
Wolfgang Holzer
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The 13C nuclear magnetic resonance spectra of 17 3,6-disubstituted pyridazine derivatives have been systematically analyzed. Chemical shifts and various 13C, 1H coupling constants are reported. Attempts were made to correlate these data with results obtained from semiempirical molecular orbital calculations as well as with substituent electronegativities and Taft's substituent constants σI and σR0. Key words: 3,6-disubstituted pyridazines, 13C NMR spectroscopy, 13C, 1H spin coupling constants.

Long-range 13C, 13C spin–spin coupling constants in anisole and some derivatives

1988 ◽  
Vol 66 (7) ◽  
pp. 1635-1640 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Methoxy Group ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Nuclear Magnetic

13C nuclear magnetic resonance chemical shifts and nJ(13C,13C) are reported for anisole and 16 of its derivatives, all enriched with 13C in the methoxyl group. 5J(13C,13C) is directly proportional to sin2θ, where θ is the angle by which the methoxy group twists about the C(1)—O bond. In acetone-d6 solution, 5J(C,C) is not observable for a number of 4-substituted anisoles, except for 1,4-dimethoxybenzene. For the latter, 5J(C,C) is compatible with a twofold barrier of 19.3 ± 1.1 kJ/mol hindering rotation about the C(1)—O bond. However, it is unlikely that the barrier is purely twofold in nature. The observed 5J(C,C) is also compatible with 10.5 and 6.0 kJ/mol for the twofold and fourfold components, respectively, implying a dynamical nuclear magnetic resonance barrier of less than 13 kJ/mol. While phase and solvent effects on the internal barrier in anisole are certainly substantial, it appears that a fourfold component must also be present. The apparent twofold barrier in 2,6-difluoroanisole is 5.4 ± 0.9 kJ/mol, based on 5J(C,C) and 6J(H-4,13C). The latter coupling constant is also reported for 1,2,3-trimethoxybenzene and used to deduce its conformation. The θ dependence of 3J(C,C) and 4J(C,C) is briefly discussed for symmetrical anisole derivatives. Differential 13C, 13C isotope shifts are reported for 1,4-dimethoxybenzene.

Review lecture: Nuclear magnetic resonance spectroscopy in two frequency dimensions

1980 ◽  
Vol 373 (1753) ◽  
pp. 149-178 ◽  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Past History ◽  
Dimensional Space ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Resonance Spectroscopy ◽  
Experimental Conditions ◽  
Nuclear Magnetic

A spectrum is normally thought of in terms of a graph of absorption intensity as a function of frequency, and in this form it has served us well for many years. A recent development extends this idea into a second frequency dimension, the spectrum now being represented by a surface in three-dimensional space. The examples are in the field of high resolution nuclear magnetic resonance (n.m.r.) spectroscopy, although the principle is rather more general, being based on the two-dimensional Fourier transformation of a transient response that is a function of two independent time variables t 1 and t 2 . By arranging for different experimental conditions to prevail during t 1 and t 2 , it is possible to separate different n.m.r. parameters, for example chemical shifts and spin coupling constants, into the two frequency dimensions. There is also an important element of correlation involved, since during t 2 the nuclei ‘remember’ their past history during t 1 ,and this has been used to correlate proton and carbon-13 chemical shifts.

Nuclear Magnetic Resonance Study of the Hydrolysis of Diethyl Methylphosphonite

1968 ◽  
Vol 22 (2) ◽  
pp. 95-98 ◽  
Author(s):  
Kenneth E. Daugherty ◽  
William A. Eychaner ◽  
John I. Stevens
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Analytical Data ◽  
Nuclear Magnetic Resonance Study ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Proton Nuclear Magnetic Resonance ◽  
Spin Spin Coupling ◽  
Nuclear Magnetic

The products of the hydrolysis reactions of diethyl methylphosphonite at room temperature have been elucidated by means of proton nuclear magnetic resonance. The reaction was followed by observing the methyl-hydrogen resonance, phosphorus-hydrogen resonance, methylenehydrogen resonance, and hydroxyl-hydrogen resonance. Upon addition of up to one mole of water per mole of diethyl methylphosphonite, ethyl hydrogen methylphosphinate was produced in a very rapid and complete reaction. Upon addition of greater than one mole of water—up to two moles of water per mole of diethyl methylphosphonite—the ethyl hydrogen methylphosphinate that was produced was further hydrolyzed to dihydrogen methylphosphinate in a very slow reaction. At ratios of two or more moles of water per mole of diethyl methylphosphonite, only dihydrogen methylphosphinate and ethanol were observed in solution after the reactions had come to completion. Trivalent phosphorus hydrolysis products were not observed in this reaction sequence. The chemical shifts, spin—spin coupling constants, and analytical data are described.

Studies of specifically fluorinated carbohydrates. Part I. Nuclear magnetic resonance studies of hexopyranosyl fluoride derivatives

1969 ◽  
Vol 47 (1) ◽  
pp. 1-17 ◽  
Author(s):  
L. D. Hall ◽  
J. F. Manville ◽  
N. S. Bhacca
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Angular Dependence ◽  
Chemical Shifts ◽  
Relative Orientation ◽  
Coupling Constants ◽  
Pyranose Ring ◽  
Spectral Parameters ◽  
Magnetic Resonance Studies ◽  
Nuclear Magnetic

A detailed study has been made of both the 1H and 19F nuclear magnetic resonance (n.m.r.) spectra of a series of hexopyranosyl fluoride derivatives. Some of the 1H spectra were measured at 220 MHz. The 1H spectral parameters define both the configuration and the conformation of each of these derivatives. Study of the 19F n.m.r. parameters revealed several stereospecific dependencies. The 19F chemical shifts depend upon, (a) the orientation of the fluorine substituent with respect to the pyranose ring and, (b) the relative orientation of other substituents attached to the ring; for acetoxy substituents, these configurational dependencies appear to be additive. The vicinal19F–1H coupling constants exhibit a marked angular dependence for which Jtrans = ca. 24 Hz whilst Jgauche = 1.0 to 1.5 Hz for [Formula: see text] and 7.5 to 12.6 Hz for [Formula: see text] The geminal19F–1H couplings depend on the orientation of the substituent at C-2; when this substituent is equatorial JF,H is ca. 53.5 Hz and when it is axial the value is ca. 49 Hz.

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