scholarly journals Long-range proton–carbon coupling constants for the determination of the stereochemical structure of organic compounds.

2021 ◽  
pp. 125-131
Author(s):  
Anwar, E. M. Noreljaleel
Keyword(s):  
Nmr Spectroscopy ◽  
Organic Compounds ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spectroscopy Method ◽  
Stereochemical Structure ◽  
New Methods ◽  
Spin Coupling Constants

A new methods for elucidating stereochemistry of organic compounds was developed on the basis of long-range proton–carbon coupling constants (2,3JC,H) and interpreting spin-coupling constants (3JH,H). Reaction of compound containing pyrin ring with nucleophile reagent was done to open the ring. HSQC-TOCSY experiments one of the new NMR spectroscopy method used to measure this values of spin-coupling constants and elucidating the stereochemistry of the product.

Determination of Absolute Signs of 119Sn-117Sn Spin-Spin Coupling Constants

1994 ◽  
Vol 49 (10) ◽  
pp. 1407-1409 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Gerald Kehr
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Two Dimensional ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
First Time

AbstractIf for a given system two-dimensional (2D) 119Sn/1H heteronuclear shift correlations can be established for long range coupling constants nJ(119Sn,1H) (n = 4, 6), absolute signs of coupling constants J(Sn,Sn) are accessible by this technique for the first time. This has been demonstrated for tetrakis(trimethylstannyl)allene (1) with 2J(119Sn,117Sn) (>0) and 4J(Sn. 117Sn) (<0) and for tris(trimethylstannyl)phosphane (2) and bis(trimethvlstannyl)- sulfane (3) with 2J(119Sn,117Sn) (<0).

scholarly journals Signs of proton–proton and proton–fluorine spin–spin coupling constants in 2-fluoro-3-methylpyridine. Sigma and pi contributions to coupling in a nitrogen heterocycle

1969 ◽  
Vol 47 (9) ◽  
pp. 1507-1514 ◽  
Author(s):  
T. Schaefer ◽  
S. S. Danyluk ◽  
C. L. Bell
Keyword(s):  
Nitrogen Atom ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nitrogen Heterocycle ◽  
Triple Resonance ◽  
Triple Resonance Experiments ◽  
Proton Proton ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The signs of all proton–proton and proton–fluorine spin–spin coupling constants in 2-fluoro-3-methylpyridine have been determined by double and triple resonance experiments. The signs of the longrange coupling constants, JH,CH3 and JF,CH3 are the same as in fluorotoluene derivatives. Their magnitudes are consistent with the assumption that the nitrogen atom primarily polarizes the σ bonds in the molecule, leaving the π contribution to the long-range coupling relatively unaffected.

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.

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