Conformation of zearalenone in solution: A vicinal coupling constant and molecular mechanics study

1990 ◽  
Vol 28 (8) ◽  
pp. 665-667 ◽  
Author(s):  
Luis Muñoz ◽  
Ricardo Riguera
Keyword(s):  
Molecular Mechanics ◽  
Coupling Constant ◽  
Vicinal Coupling Constant

Long-range coupling and conformation in some thienylmethylene and furfurylidene derivatives

1977 ◽  
Vol 30 (2) ◽  
pp. 357 ◽  
Author(s):  
GC Brophy ◽  
PJ Newcombe ◽  
RK Norris
Keyword(s):  
Aromatic Ring ◽  
Long Range ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Vicinal Coupling Constant

The p.m.r, spectra of 12 2-thienylmethylene and furfurylidene derivatives are reported. The average conformation about the Ar-CHXY bond is deduced from the magnitude of the meta (and ortho) long-range benzylic coupling constants. In thiophens, conformations in which the benzylic hydrogen is in or near the plane of the aromatic ring and anti to the ring sulphur are preferred. In furans the hydrogen-in-plane conformations are again favoured. The signs of the meta and ortho benzylic coupling constants have been determined and are positive and negative respectively with respect to the vicinal coupling constant J3,4.

NMR Spectroscopic Studies of Thialene (Cyclopenta[b]thiapyran) and Isothialene (Cyclopenta[c]thiapyran)

1993 ◽  
Vol 58 (1) ◽  
pp. 113-120 ◽  
Author(s):  
Robert F. X. Klein ◽  
Václav Horák ◽  
Arthur G. Anderson
Keyword(s):  
Chemical Shift ◽  
Bond Order ◽  
Spectroscopic Studies ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Vicinal Coupling Constant ◽  
Spectral Parameters ◽  
First Order ◽  
Nmr Techniques ◽  
C Nmr

1H and 13C NMR spectral parameters are reported for the S-pseudoazulenes thialene (cyclopenta[b]thiapyran) (I) and isothialene (cyclopenta[c]thiapyran) (II). Both compounds display complex first order spectra, with thialene having 10 and isothialene 14 of 15 possible coupling constants. Complete unambiguous assignments of all protons and non-quaternary carbons were made via 2-dimensional NMR techniques and PPP-SCF π-electron density/chemical shift and π-bond order/vicinal coupling constant correlations.

Reaction of carbanions generated from arylmethylphosphonates with cyclic enones. Regio- and stereoselectivity of addition

1998 ◽  
Vol 76 (10) ◽  
pp. 1344-1351 ◽  
Author(s):  
Agnes M Modro ◽  
Tom A Modro ◽  
Malose J Mphahlele ◽  
Wieslawa Perlikowska ◽  
André Pienaar ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Crystal And Molecular Structure ◽  
Addition Product ◽  
Coupling Constant ◽  
Vicinal Coupling Constant ◽  
Relative Configuration ◽  
H Nmr ◽  
Li Po ◽  
Cyclic Enones ◽  
C Nmr

α-Lithiated benzylphosphonate esters, XC6H4CH(Li)PO3Et2, add regioselectively to cyclohex-2-enone at the carbonyl group; higher reaction temperatures lead to the reversal to the starting materials, and not to the 1,4-addition. Relative configuration of the C(1) and Cα centers in the 1,2-adducts was determined from the 13C NMR spectra. For 2-methylcyclohex-2-enone the regioselectivity of the addition is decreased. The lithioderivative of diethyl 1-naphthylmethylphosphonate, C10H7CH(Li)PO3Et2, shows reverse regioselectivity yielding the 1,4-, but not the 1,2- addition product. The crystal and molecular structure of that 1,4-adduct has been determined and demonstrates that the conformation about the C(1)-Cα bond is close to that existing in solution, deduced from the value of the 1H NMR 3JHH vicinal coupling constant of the H(1)-C(1)-Cα-H hydrogens. The same conformation was also confirmed as the most stable by molecular modeling. Key words: α-lithiated arylmethylphosphonates, 1,2- vs. 1,4-addition to cyclic enones, steric effects of the cyclohex-2-enone, molecular structure and molecular modelling of the 1,4-adduct of 1-naphthylmethylphosphonate to cyclohex-2-enone.

Effect of solvent and temperature upon the rotationally averaged vicinal coupling constants of some substituted 1,2-dibromoethanes

1969 ◽  
Vol 47 (8) ◽  
pp. 1295-1309 ◽  
Author(s):  
W. F. Reynolds ◽  
D. J. Wood
Keyword(s):  
Coupling Constants ◽  
Dipolar Interactions ◽  
Coupling Constant ◽  
Vicinal Coupling Constant ◽  
Factors Affecting ◽  
Relative Stabilities ◽  
Vicinal Coupling Constants ◽  
Solvent Dependence ◽  
Rotational Equilibrium ◽  
The Difference

The solvent dependence of vicinal coupling constants has been investigated for (1,2-dibromoethyl)-benzene and three of its 4-substituted derivatives and for threo- and erythro(1,2-dibromopropyl)benzene. The temperature dependence of the vicinal coupling constants of three of the compounds has also been investigated. The difference between the two vicinal coupling constants of (1,2-dibromoethyl)benzene is dependent upon solution dielectric constant (in non-aromatic solvents) while the sum of coupling constants remains constant. The relative stabilities of its three rotamers are deduced from this information. A polar substituent in the 4-position does not affect the rotational equilibrium in any predictable manner. The vicinal coupling constant of threo(1,2-dibromopropyl)benzene is strongly solvent dependent. The relative stabilities of its three rotamers are deduced from the observation that the vicinal coupling constant is temperature independent. The most stable rotamer of erythro(1,2-dibromopropyl)-benzene is deduced from the observation that the vicinal coupling constant is large and independent of solvent. Factors affecting conformational preference are deduced. It is concluded that dipolar interactions are as important as steric interactions.

Determination of erythro and threo configurations by nuclear magnetic resonance spectroscopy

1968 ◽  
Vol 46 (21) ◽  
pp. 3415-3418 ◽  
Author(s):  
George H. Schmid
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Resonance Spectroscopy ◽  
Coupling Constant ◽  
Vicinal Coupling Constant ◽  
Nuclear Magnetic Resonance Spectra ◽  
Threo Isomer ◽  
Isomeric Pairs ◽  
Nuclear Magnetic

An examination of the nuclear magnetic resonance spectra of ten pairs of racemic erythro and threo isomers of 1,2-disubstituted-1-arylpropanes shows that the signals of the methyl protons of the erythro isomer always appear at lower field than the threo isomer. The vicinal coupling constant (Jab) of the erythro isomer is found to be smaller than that of the threo isomer in six of the isomeric pairs indicating that the magnitude of Jab is a poor criterion of configuration of the 1,2-disubstituted-1-arylpropanes.

Stereoselective synthesis and stereochemistry of r-2-alkoxycarbonyl-c-3-o-substituted phenyl-1,4-thiazane 1,1-dioxides

2005 ◽  
Vol 83 (3) ◽  
pp. 202-208
Author(s):  
N Bhavani ◽  
S Perumal ◽  
R Banureka
Keyword(s):  
Long Range ◽  
Trans Isomer ◽  
Stereoselective Synthesis ◽  
Nmr Assignments ◽  
Chair Conformation ◽  
Coupling Constant ◽  
Vicinal Coupling Constant ◽  
Relative Configuration ◽  
Cis Isomer ◽  
C Nmr

r-2-Alkoxycarbonyl-c-3-aryl-1,4-thiazane 1,1-dioxides were obtained as the stereoselective product, when the aldehyde used was o-substituted benzaldehyde while the p-substituted benzaldehydes gave a trans product. The relative configuration of the adjacent alkoxycarbonyl and aryl groups was assigned from the vicinal coupling constant, 3J = 10.6 Hz in the trans isomer and 3.2 Hz in the cis isomer, and from the multiplicity pattern, i.e., a doublet for the H-2 proton of the trans isomer and a triplet for the H-2 proton of the cis isomer. The unusual, large long-range coupling (4J = 2.8 Hz) because of the "W" arrangement between H-2e and H-6e across the ring type was very useful for confirming the cis configuration and chair conformation of the isomer. The various 1H and 13C NMR assignments were made with the help of 1H–1H COSY, 1H–13C COSY, HMBC, and NOESY spectral analyses.Key words: 1H and 13C NMR, 1H–1H COSY, 1H–13C COSY, HMBC, NOESY, stereoselectivity, 1,4-thiazane.

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