PROTON MAGNETIC RESONANCE MEASUREMENTS OF FORMAMIDE

The high-resolution proton resonance spectrum of formamide has been measured and analyzed. Quadrupole broadening of the resonance signals due to the N14 nucleus was eliminated by substitution of the isotopic nucleus N15. Twenty-four lines were resolved in the spectrum, which is consistent with restricted rotation about the C—N bond. The non-equivalence of the two protons in the N15H2 group is characterized by a smaller screening constant and a greater spin–spin interaction of the proton which is in the trans position relative to the carbonyl group. It is suggested this difference in the spin coupling of the two protons may be associated with different N—H bond lengths. Pronounced changes in the chemical shifts and spin-coupling constants result when formamide is dissolved in dilute solution in water and acetone. In water solution the relative magnitudes of the spin coupling of the two protons in the NH2 group is reversed from that observed in pure formamide and the coupling of the aldehyde proton to N15 varies by nearly 50%. Heating of formamide above room temperature causes rotation of the NH2 group as well as proton exchange between neighboring molecules. The two effects could be separated. From the observed changes in the proton spectra as a function of temperature the barrier hindering rotation (measured in a 10 mole% solution of formamide in acetone) was found to be 18 ± 3 kcal/mole. The activation energy for proton exchange in pure liquid formamide was found to be 10 ± 3 kcal/mole.

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Nuclear Magnetic Resonance Spectrum of 1-Hydroxy-2,3-Epoxypropane

Applied Spectroscopy ◽

10.1366/000370268774384227 ◽

1968 ◽

Vol 22 (6) ◽

pp. 773-776

Author(s):

A. Leifer ◽

H. L. Goldstein

Keyword(s):

Resonance Spectrum ◽

Chemical Shifts ◽

Internal Standard ◽

Coupling Constants ◽

Spin Coupling ◽

Pure Liquid ◽

Nmr Spectrum ◽

Hydroxyl Proton ◽

Spin Coupling Constants ◽

Experimental Values

The NMR spectrum of pure liquid 1-hydroxy-2,3-epoxypropane has been analyzed quantum mechanically. The analysis is greatly simplified by treating the protons on the propane chain as two separate ABX systems. The chemical shifts at 60 Mcps, relative to the internal standard tetramethylsilane (TMS), and the spin coupling constants were found to be vA = 168.1 cps, vB = 160.5 cps, vX = 188.8 cps, vA' = 232.2 cps, vB' = 212.8 cps, JAB = 5.2 cps, JA'B' = 12.7 cps, JXA = 4.5 cps, JXA' = 2.9 cps, JBX = 2.7 cps, JB'X = 5.3 cps. Using these parameters the calculated frequencies of the spectrum are in excellent agreement with the experimental values. The chemical shift of the hydroxyl proton was found to be 266.8 cps downfield from TMS.

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Anisotropies in spin—spin coupling constants and chemical shifts as determined from the NMR spectra of molecules oriented by liquid crystal solvents

Progress in Nuclear Magnetic Resonance Spectroscopy ◽

10.1016/0079-6565(82)80004-6 ◽

1982 ◽

Vol 15 (3) ◽

pp. 249-290 ◽

Cited By ~ 93

Author(s):

J. Lounila ◽

J. Jokisaari

Keyword(s):

Liquid Crystal ◽

Nmr Spectra ◽

Chemical Shifts ◽

Coupling Constants ◽

Spin Coupling ◽

Spin Coupling Constants ◽

Spin Spin Coupling

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

Organic Chemistry Frontiers ◽

10.1039/d1qo00034a ◽

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...

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

Canadian Journal of Chemistry ◽

10.1139/v57-196 ◽

1957 ◽

Vol 35 (12) ◽

pp. 1487-1495 ◽

Cited By ~ 60

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.

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The planar conformation of 2-methylthiobenzaldehyde in solution

Canadian Journal of Chemistry ◽

10.1139/v83-005 ◽

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.

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Semiempirical calculation of 29Si NMR chemical shifts and 29Si-13C spin-spin coupling constants in some substituted bridgehead polycycloalkanes

Journal of Molecular Structure THEOCHEM ◽

10.1016/0166-1280(94)80021-9 ◽

1994 ◽

Vol 304 (3) ◽

pp. 247-254 ◽

Cited By ~ 9

Author(s):

D. Kovaček ◽

Z.B. Maksić ◽

S. Elbel ◽

J. Kudnig

Keyword(s):

Chemical Shifts ◽

Semiempirical Calculation ◽

Coupling Constants ◽

Spin Coupling ◽

29Si Nmr ◽

Nmr Chemical Shifts ◽

Spin Coupling Constants ◽

Spin Spin Coupling

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

Zeitschrift für Naturforschung B ◽

10.1515/znb-1979-1124 ◽

1979 ◽

Vol 34 (11) ◽

pp. 1606-1611 ◽

Cited By ~ 11

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.

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

Zeitschrift für Naturforschung B ◽

10.1515/znb-1982-0518 ◽

1982 ◽

Vol 37 (5) ◽

pp. 631-645 ◽

Cited By ~ 35

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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