Journal ArticleDOI
Calculation of gauche coupling constants from substituent electronegativities
TLDR
In this paper, a method for the calculation of gauche coupling constants from substituent electronegativities by taking into account the orientation of the substituents is described.Abstract:
The calculation of gauche coupling constants from substituent electronegativities by a method which takes into account the orientation of the substituents is described. This correlation has been derived from the coupling constants of disubstituted ethanes and has been applied to the calculation of coupling constants in cyclohexanes and 6-membered heterocycles. The detection of angular distortion in 6-membered rings from the difference between calculated and observed coupling constants is also described.read more
Citations
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Stereochemical aspects of proton chemical shifts. III—Configurational assignments in pentacyclic systems without recourse to a karplus equation
TL;DR: In contrast to the use of coupling constants, chemical shift criteria may lead to unambiguous structural elucidations in pseudorotational frameworks (pentacycles, heptacycles etc.).
Journal ArticleDOI
Dynamic proton magnetic resonance studies on complex spin systems. Non‐mutual three‐spin exchange in four 1‐substituted cyclohexanes‐2,2,3,3,4,4,5,5‐d8 and mutual four‐spin exchange in cyclohexane‐1,1,2,2,3,3,4,4‐d8
TL;DR: The intrinsic advantage of coupled three-proton spin systems in the quantitative study of conformational equilibria and equilibrations, as elaborated and exemplified in the preceding publication, is exploited for the determination of precise thermodynamic and dynamic parameters for octadeuteriocyclohexanes containing a cyano, chloro, bromo or deuteriomethoxy substituent and hydrogen atoms on the substituted and on one contiguous carbon as discussed by the authors.
Journal ArticleDOI
Benzylidene acetal structural elucidation by N.M.R. Spectroscopy: Application of carbon-13. N.M.R.-Spectral parameters
TL;DR: In this article, the 13 C-n.m.r. spectra of 19 2-phenyl-1,3-dioxolane derivatives were examined and it was found that both the 13 c-n-m. r. chemical shift for the acetal carbon atom and the one-bond coupling constant between the aceta and the proton had values that could be used to distinguish between acetals having different ring sizes.
Journal ArticleDOI
Two novel diterpenes from the roots of Phyllanthus acidus (L.) Skeel
Thuc-Huy Duong,Xuan-Hao Bui,Pierre Le Pogam,Huu-Hung Nguyen,Thi-Thuan Tran,Thi-Anh-Tuyet Nguyen,Warinthorn Chavasiri,Joël Boustie,Kim-Phi-Phung Nguyen +8 more
TL;DR: In this article, two new diterpenes, phyllanes A and B, were isolated from the roots of Phyllanthus acidus, along with the cleistanthane diterpene, spruceanol.
Journal ArticleDOI
Conformational studies on 2‐fluoro‐1,2‐disubstituted ethanes by NMR spectroscopy. Influence of electronegativity on vicinal proton–proton and fluorine–proton coupling constants
Abstract: The analysis of the ABKX spectra of thirteen compounds of the series RC(H-K)(F-X)C(H-A)(H-B)X gave the four vicinal proton-proton and fluorine-proton coupling constants. These coupling constants of conformationally mobile structures were used (i) to calculate the populations of the rotational states of the CHFCH2 bond, (ii) to calculate the vicinal trans proton-proton J(HH)t and gauche and trans fluorine-proton coupling constants J(FH)g and J(FH)t and (iii) to give the unambiguous assignment of protons H-A and H-B. The dependence of the gauche and trans coupling constants with substituent electronegativity is explored. The results extend known correlations towards smaller electronegativity values. More quantitatively, the results and those in the literature, excluding those where deformations of torsional or bond angles occur, give a good fit of the data: a linear fit for J(HH)t = 15.0-0.77 Σ(ΔE), an exponential fit for J(FH)g = 15.35 exp [-0.266 Σ (ΔE)] and a linear fit for J(FH)t = 65.75 - 7.52 Σ (ΔE), where Σ (ΔE) is the sum of the electronegativity difference between hydrogen and the six atoms or groups on the CHCF fragment.
References
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Contact Electron‐Spin Coupling of Nuclear Magnetic Moments
TL;DR: In this article, the valence-bond theory for the contact electron-spin coupling of nuclear magnetic moments is used to calculate the proton−proton, proton-fluorine, and fluorine-florine coupling constants in ethanic and ethylenic molecules.