SPIN ECHOES IN ALCOHOLS AND DERIVATIVES

1956 ◽  
Vol 34 (7) ◽  
pp. 653-667 ◽  
Author(s):  
G. J. B. Crawford ◽  
J. S. Foster
Keyword(s):  
Chemical Shifts ◽  
Spin Echo ◽  
Larmor Frequency ◽  
Molecular Structures ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hydroxyl Group ◽  
Primary Alcohols ◽  
Field Evidence ◽  
Spin Echo Technique

The spin echo technique has been employed to measure the relative chemical shifts and the indirect spin–electron–spin coupling constants between protons at different structural sites in ethyl, propyl, isopropyl, butyl, isobutyl, and amyl alcohols and certain of their derivatives at a Larmor frequency of 29.0 Mc./s. The separation between the two r-f. pulses applied to the sample increases regularly in accurately known steps which are controlled electronically. Thus the frequencies modulating the echo envelope have been readily measured with a precision as high as 4% in favorable cases. Relative chemical shifts found by slow passage experiments have been checked with higher accuracy, particularly for the primary alcohols. Encouraged by the implications of these earlier data, we have here analyzed the longer hydrocarbon chains on the basis of the theoretical computations of Hahn and Maxwell for only two groups of non-equivalent protons. This more precise investigation confirms the assumptions made as to where the major shifts and couplings do and do not exist in the molecular structures. In the halide molecules, it is found that the observed relative chemical shifts are linearly proportional to the paramagnetic fields arising from the valence orbits of the halogens polarized by the external field. Evidence for the particular J-coupling to the hydroxyl group in the alcohols suggests that this bond is effectively stronger in the heavier molecules which are only slightly soluble in water.

73 Ge Nuclear Magnetic Resonance Studies

1971 ◽  
Vol 26 (9) ◽  
pp. 1384-1389 ◽  
Author(s):  
J . Kaufmann ◽  
W. Sahm
Keyword(s):  
Chemical Shifts ◽  
Spin Echo ◽  
Relaxation Times ◽  
Least Square ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nmr Spectrum ◽  
Spin Coupling Constants ◽  
Spin Echo Technique ◽  
Spin Spin Coupling

Abstract The 73Ge spectra of some germanium-tetra-halides, germanium-tetra-alkyles, and of germanium-tetra-methoxide have been observed. The chemical shifts of these 73Ge NMR-lines were measured as functions of the temperature in the range up to 50 °C. In CS2-and benzene-solutions of Gel4 , two 73Ge-lines were found. The 73Ge NMR-spectrum of Ge(CH3)4 caused by indirect spin-spin-coupling between the 73Ge nucleus and the protons is well resolved. The spin-spin-coupling constants of Ge(CH3)4 and of Ge(OCH3)4, which shows an unresolved spectrum, were evaluated by an iterative least square fitting routine. The relaxation times T2 (in the range 30...740 msec) measured by the Carr-Purcell spin-echo-technique and calculated from the line widths are in good agreement. Precision measurements of the ratios of the Larmor frequencies of 73Ge in GeCl4, 41K in aqueous KF-solution and 2H in pure heavy water lead to a magnetic moment of 73Ge: μ = -(0.876 78 ± 0.000 01) μN (uncorrected).

Structural Characterization of Natural Products By Means of Quantum Chemical Calculations of NMR Parameters: New insights

2021 ◽  
Author(s):  
Fabio Luiz Paranhos Costa ◽  
Ana Carolina Ferreira de Albuquerque ◽  
Rodolfo Goetze Fiorot ◽  
Luciano Morais Lião ◽  
Lucas Haidar Martorano ◽  
...  
Keyword(s):  
Natural Products ◽  
Structural Characterization ◽  
Quantum Chemical ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nmr Parameters ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The calculation of NMR parameters for natural products was pioneered by Bifulco and coworkers in 2002. Since then, modelling 1H and 13C chemical shifts and spin-spin coupling constants for this...

THE ANALYSIS OF NUCLEAR MAGNETIC RESONANCE SPECTRA: III. PYRIDINE AND DEUTERATED PYRIDINES

1957 ◽  
Vol 35 (12) ◽  
pp. 1487-1495 ◽  
Author(s):  
W. G. Schneider ◽  
H. J. Bernstein ◽  
J. A. Pople
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
High Resolution ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Calculated Spectrum ◽  
Proton Resonance ◽  
Nuclear Magnetic Resonance Spectra ◽  
Spin Coupling Constants

The proton resonance spectra of pyridine, 2,6-pyridine-d2, 3-pyridine-d1, and 4-pyridine-d1 have been obtained for the pure liquids under conditions of high resolution. The spectra have been analyzed as proton groupings of AB2X2, AB2, perturbed ABX, and B2X2 respectively. The spin-coupling constants obtained from analysis of the simpler spectra of the deuterated molecules were used to suggest trial solutions for the analysis of the complicated AB2X2 spectrum of pyridine. A final set of chemical shifts and spin-coupling constants derived for pyridine give satisfactory agreement between the observed and calculated spectrum.

In-plane and out-of-plane conformational preferences of the sulfhydryl group in some halothiophenol derivatives

1979 ◽  
Vol 57 (12) ◽  
pp. 1421-1425 ◽  
Author(s):  
Ted Schaefer ◽  
William J. E. Parr
Keyword(s):  
Sulfhydryl Group ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hydroxyl Group ◽  
Recent Analysis ◽  
Phenol Derivatives ◽  
Out Of Plane ◽  
Intramolecular Hydrogen ◽  
Cis And Trans ◽  
Spin Spin Coupling

Long-range spin–spin coupling constants between sulfhydryl protons and ring protons in some halothiophenol derivatives in CCl4 solutions are reported. In contrast to the corresponding phenol derivatives, substantial amounts of out-of-plane conformers are present at 305 K for all but 2,6-dichlorothiophenol. The cis and trans conformers differ by only about 0.2 kcal/mol in free energy for 2,4-dibromothiophenol and 2,4-dichlorothiophenol, in good agreement with a recent analysis of the dipole moment observed for the latter compound. The barrier to internal rotation of the sulfhydryl group is considerably smaller than for a hydroxyl group and rough estimates are given for the barrier in a few compounds. For example, the barrier in 2,3,5,6-tetrafluorothiophenol is lower than in 2,6-dichlorothiophenol. STO-3G MO calculations overestimate the internal barrier to rotation of the sulfhydryl group, but yield charge densities for this group which indicate that a major cause of the relative weakness of its intramolecular hydrogen bonds resides in its lack of polarity.

Indirect Nuclear Spin-Spin Coupling Constants 1J(17O,11B). First Observation And Calculation Using Density Functional Theory (Dft)

2006 ◽  
Vol 61 (8) ◽  
pp. 949-955 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Oleg L. Tok
Keyword(s):  
Density Functional ◽  
Reasonable Agreement ◽  
Bond Angle ◽  
Calculated Data ◽  
Molecular Structures ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Functional Theory ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Coupling constants 1J(17O,11B) of borates, borane adducts and boranes with boron-oxygen bonds have been calculated on the basis of optimised molecular structures using the B3LYP/6-311+G(d,p) level of theory. This indicates that such coupling constants can be of either sign and that their magnitudes can be rather small. Since both 11B and 17O are quadrupole nuclei, it is therefore difficult to measure representative data. In the cases of trimethoxyborane and tetraethyldiboroxanes, it proved possible to obtain experimental data 1J(17O,11B) (22 and 18 Hz) by measurement of 17O NMR spectra at high temperature (120 °C and 160 °C) respectively. The magnitude of these coupling constants is in reasonable agreement with calculated data. In the case of the diboroxane, this points towards a bond angle B-O-B more close to 180◦ than to 140°

The planar conformation of 2-methylthiobenzaldehyde in solution

1983 ◽  
Vol 61 (1) ◽  
pp. 26-28
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spectral Parameters ◽  
H Nmr ◽  
Heavy Atoms ◽  
Planar Conformation ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Infrared Data

The 1H nmr spectral parameters are extracted for a 4 mol% solution of 2-methylthiobenzaldehyde in CCl4 at 305 K. The long-range spin–spin coupling constants involving the aldehydic and methyl protons are consistent only with a preferred conformation in which all heavy atoms are coplanar, as are the chemical shifts of the ring and methyl protons. This conclusion contradicts previous interpretations of the dipole moment, the nmr parameters, and of the infrared data for CCl4 solutions. The present data show that the O-syn and O-anti forms of the compound are present in roughly equal proportions.

Zur Struktur des Enols von Benzoylaceton / On the Structure of the Enol of Benzoylacetone

1979 ◽  
Vol 34 (11) ◽  
pp. 1606-1611 ◽  
Author(s):  
W. Winter ◽  
K.-P. Zeller ◽  
S. Berger
Keyword(s):  
Structural Model ◽  
Chemical Shifts ◽  
Ring System ◽  
Coupling Constants ◽  
Spin Coupling ◽  
X Ray ◽  
Wide Range ◽  
Spin Coupling Constants ◽  
C Nmr ◽  
Oxygen Atoms

Abstract A low temperature X-ray study of the enol of benzoylacetone indicates fixed positions of the C and O atoms within the enolic ring system and an extensive bond delocalisation over these atoms. The distribution of electron density between the two oxygen atoms shows that the enolic hydrogen is spread over a wide range. This is in accordance with a structural model proposed by de la Vega, whereupon the C and O atoms are kept fixed in their average positions during a tunneling process of the hydrogen between the two oxygen atoms. With this conception, the chemical shifts in the 17O and 13C NMR spectra, the 13C13C spin coupling constants and the temperature independance of these values can be explained.

A Comparative Study of Metal Shielding in Low Valent Vanadium, Niobium and Manganese Complexes

1982 ◽  
Vol 37 (5) ◽  
pp. 631-645 ◽  
Author(s):  
Dieter Rehder ◽  
Hans-Christoph Bechthold ◽  
Ahmet Keçeci ◽  
Hartwig Schmidt ◽  
Michael Siewing
Keyword(s):  
Comparative Study ◽  
Nuclear Spin ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Manganese Complexes ◽  
Ligand Field ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Ligand Bond

Variations of the metal chemical shifts δ(51V), δ(55Mn) and δ(93Nb) with the paramagnetic deshielding contribution to the overall shielding are discussed in terms of influences imposed by the ligand field splitting, the nephelauxetic effect and the covalency of the metal-to-ligand bond. Complexes under investigation are isoelectronic and/or iso-structural series [M(CO)6-nLn]q (M = V, Nb: q = -1; M = Mn: q = + 1; n = 0-6), η5-C5H5M(CO)4-nLn (M = V, Nb; n = 0-4) and η5-C5H5M(L')2L (M = V, L' = NO; M = Mn, L' = CO). L is a monodentate or l/n oligodentate phosphine. η varies with the point symmetry of the complex, and with ligand parameters of primarily electronic or steric origin. Generally, for weak to medium π-interaction, there is a decrease of shielding with decreasing π-acceptor power of the ligand, increasing ligand bulkiness, increasing ring strains in chelate structures and increasing degree of substitution. For strong π-interaction, the trends may be interconverted. PF3 is shown to be a slightly weaker π-acceptor than CO. Selected results on nuclear-spin spin coupling constants, 13C and 31P shielding are also presented

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