Spin–spin coupling constants between side-chain and ring fluorine nuclei in some benzotrifluoride, benzal fluoride, and benzyl fluoride derivatives: coupling mechanisms

1979 ◽  
Vol 57 (7) ◽  
pp. 807-812 ◽  
Author(s):  
Ted Schaefer ◽  
Walter Niemczura ◽  
Chiu-Ming Wong ◽  
Kirk Marat
Keyword(s):  
Nmr Spectra ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Complete Analysis ◽  
Side Chain ◽  
Coupling Mechanism ◽  
Conformational Preferences ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms

A complete analysis of the 1H and 19F nmr spectra of 2,5- and 3,4-difluorobenzotrifluoride, together with multiple resonance experiments, yields the signs and magnitudes of the long-range 19F,19F and 1H,19F spin–spin coupling constants. The coupling mechanisms are discussed. In particular, the coupling over six bonds, [Formula: see text], whose sign is interpretable in terms of a σ–π mechanism, is too large in magnitude when compared to [Formula: see text], and [Formula: see text] in the analogous compounds. These latter three couplings are consistent in sign and magnitude with what is known about hyperfine interaction constants. The magnitudes of [Formula: see text] are reported for 4-fluorobenzotrifluoride, 3-amino-4-fluorobenzotrifluoride, 3-nitro-4-fluorobenzotrifluoride, as are 6JpF,F values for p-fluorobenzal fluoride and p-fluorobenzyl fluoride. In contrast to 6JpH,CH and 6JpF,CH it seems unlikely that, unless its coupling mechanism becomes more precisely understood, 6JpF,CF will be a reliable indicator of conformational preferences.

A proton magnetie resonance and molecular orbital study of the conformational preferences of the vinylic fragment in some 2-vinylfurans and in 2-vinylthiophene

1976 ◽  
Vol 54 (20) ◽  
pp. 3216-3223 ◽  
Author(s):  
William J. E. Parr ◽  
Roderick E. Wasylishen ◽  
Ted Schaefer
Keyword(s):  
Molecular Orbital ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Side Chain ◽  
Orbital Theory ◽  
Molecular Orbital Study ◽  
Conformational Preferences ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The stereospecific spin–spin coupling constants over five bonds between the α-proton in the side chain and the protons in the heterocycle in 2-vinylfuran, in its β-nitro and β-aldehydic derivatives, and in 2-vinylthiophene are used to demonstrate the preponderance of the s-trans conformers in polar and nonpolar solutions. These conclusions are compared with predictions made by molecular orbital theory at the STO-3G, INDO, CNDO/2, and MINDO/3 levels. Long-range coupling constants between the protons in the side chain and protons in the heterocycle are calculated by CNDO/2 and INDO–MO–FPT and are compared with experiment. It is concluded that the five-bond couplings involving the α-proton are most sensitive to conformation and that they are transmitted mainly via a σ electron mechanism. The other long-range coupling constants are discussed in terms of σ and π electron mechanisms. The STO-3G calculations yield barriers to internal rotation of greater than 4.8 kcal/mol.

1H and 13C nuclear magnetic resonance and molecular orbital studies of the internal rotational potential and of spin–spin coupling transmission in phenylallene

1995 ◽  
Vol 73 (9) ◽  
pp. 1478-1487 ◽  
Author(s):  
Ted Schaefer ◽  
Scott Kroeker ◽  
David M. McKinnon
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Molecular Orbital ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Side Chain ◽  
Coupling Constant ◽  
H Nmr ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms

The 1H nuclear magnetic resonance spectra of phenylallene, diluted in acetone-d6 and benzene-d6, yield long-range coupling constants over as many as eight formal bonds between the ring and side-chain protons. These are discussed in terms of σ- and π-electron spin–spin coupling mechanisms, which are sensitive to the torsion angle between the allenyl and phenyl fragments. The torsion angle is assessed by means of molecular orbital computations of the internal rotational potential, whose height is calculated as 16.0 kJ/mol at the MP2/6-31G* level of correlation-gradient theory. Comparison with experimental and theoretical internal rotational potentials for styrene suggests that steric repulsions in the planar form of styrene amount to about 4 kJ/mol. In a field of 7.0 T, phenylallene is partially aligned, entailing a positive dipolar coupling constant between the methylene protons, from which absolute signs of the spin–spin coupling constants involving these protons can be inferred. Such coupling constants over seven and eight bonds, to the meta and para protons, are taken as being mediated by the extended π-electron system, providing a measure of π-electron contributions to coupling constants between meta protons and those in side chains (spin correlation). Some coupling constants between protons and 13C nuclei in the side chain, as well as between ring protons and these 13C nuclei, are also discussed in terms of spin coupling mechanisms. Solvent perturbations of one-bond proton–carbon coupling constants in the allenyl group do not follow the usual pattern in which an increase in polarity of the solvent is associated with an increase in the magnitude of the coupling constant. Keywords: 1H NMR, phenylallene; 1H NMR, long-range spin–spin coupling constants in phenylallene; phenylallene, internal rotational potential, molecular orbital computations; molecular orbital calculations, an internal rotational potential in phenylallene.

Experimental and Theoretical-Study of Carbon-Fluorine Couplings in the NMR-Spectra of 2-Fluoroaryl Ketones

1985 ◽  
Vol 38 (12) ◽  
pp. 1779 ◽  
Author(s):  
RH Contreras ◽  
CG Giribet ◽  
MA Natiello ◽  
J Perez ◽  
ID Rae ◽  
...  
Keyword(s):  
Theoretical Study ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Side Chain ◽  
Aliphatic Carbon ◽  
Spin Coupling Constants ◽  
Fermi Contact ◽  
Spin Spin Coupling ◽  
Fermi Contact Term ◽  
Good Agreement

Calculations by the IPPP-INDO method give the spin-spin coupling constants for the side-chain carbons, 3JCF and 4JCF, as 4.97 and 6.86 Hz respectively with substantial contributions to through-space coupling from the pathway CO-C-H…F. The observed values for 1-(2- fluorophenyl ) ethanone , 3.3 and 7.2 Hz, and for 1-(2,5- difluorophenyl ) ethanone , 3.7 and 7.3 Hz, are in good agreement with these predictions. Two compounds, a dihydroindenone and a naphthalenone, in which this pathway cannot be effective, show no fluorine coupling to the aliphatic carbon next to the carbonyl and the values of 3JCF are reduced to 2.2 and 2.5 Hz, consistent with the loss of a through-space Fermi contact term of the kind described above.

NMR spectra, MO calculations of spin-spin coupling constants and conformational analysis of substituted 1,3-dioxolanes

1980 ◽  
Vol 13 (1) ◽  
pp. 17-25 ◽  
Author(s):  
Rois Benassi ◽  
Luisa Schenetti ◽  
Ferdinando Taddei ◽  
Luigi Villa ◽  
Vincenzo Ferri
Keyword(s):  
Conformational Analysis ◽  
Nmr Spectra ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Mo Calculations ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Anwendung der 15N-NMR-Spektroskopie zur Charakterisierung reaktiver, koordinativ ungesättigter Zinn-, Bleiund Phosphor-Stickstoff-Verbindungen / Application of 15N-NMR Spectroscopy to the Characterization of Reactive, Coordinatively Unsaturated Tin-, Lead- and Phosphorus-Nitrogen Compounds

1987 ◽  
Vol 42 (12) ◽  
pp. 1515-1519 ◽  
Author(s):  
Carin Stader ◽  
Bernd Wrackmeyer
Keyword(s):  
Nmr Spectra ◽  
Pulse Sequence ◽  
Coupling Constants ◽  
Spin Coupling ◽  
15N Nmr ◽  
Nmr Data ◽  
15N Nmr Spectroscopy ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

AbstractThe basic INEPT pulse sequence proved most useful for recording 15N NMR spectra at natural abundance of bis(amino)stannvlenes (1). -plumbylenes (2) and of imino-amino-λ2-phosphanes (3), where the nitrogen atoms carry bulky substituents like Me3Si-, t-Bu-, 2.4.4-trimethyl-2- pentyl-groups (t-Oct-groups) or are part of the 2.2.6.6-tetramethylpiperidinyl group. The sensitiv­ity of this technique is proved by the observation of 117/119Sn or 207Pb satellites owing to spin-spin coupling constants 1J(117/119Sn15N) and 1J(117/119Pb15N), respectively. NMR data of bis[bis(trimethylsilyl)methyl]tin (4) are reported in order to corroborate the arguments for the interpretation of the δ(15N) and 1J(119Sn15N) data. The 15N NMR data of the λ2-phosphanes (3) indicate a bonding situation similar to that in triazenes.

Long-range spin–spin coupling constants as an indicator of conformational preferences in ethyl and trifluoroethyl vinyl ethers

1977 ◽  
Vol 55 (15) ◽  
pp. 2835-2838 ◽  
Author(s):  
Ted Schaefer ◽  
William J. E. Parr
Keyword(s):  
Vinyl Ether ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Ethyl Vinyl Ether ◽  
Spectroscopic Techniques ◽  
Ethyl Vinyl ◽  
Conformational Preferences ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The observed and calculated, negative, long-range spin–spin coupling constants over five bonds between olefinic and methylene protons in ethyl vinyl ether and in 2,2,2-trifluoroethyl vinyl ether are consistent with predominant s-cis planar conformations. The five-bond couplings are sensitive to the proximity of the bonds containing the coupled nuclei and are unobservably small in 1-butene where the H,H distances are somewhat larger than in the ethers. The present results concur with the arguments based on other spectroscopic techniques.

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