ChemInform Abstract: Effect of Pressure on the Proton-Proton Vicinal Coupling Constants in 1,1,2-Trichloroethane and 1,1,2,2-Tetrachloroethane-1-13C. A New Approach to High-Pressure Study of Molecular Conformations.

ChemInform ◽  
1989 ◽  
Vol 20 (7) ◽  
Author(s):  
H. YAMADA ◽  
T. KAZUOKA ◽  
A. SERA
Keyword(s):  
High Pressure ◽  
Coupling Constants ◽  
Proton Proton ◽  
New Approach ◽  
Molecular Conformations ◽  
Effect Of Pressure ◽  
Vicinal Coupling Constants ◽  
High Pressure Study

Notiz: The Dependence of Vicinal Proton-Proton Coupling Constants of Norbomenes on Molecular Structure

1996 ◽  
Vol 51 (9) ◽  
pp. 1042-1044
Author(s):  
Zoran Marković ◽  
Stanimir Konstantinović ◽  
Ivan Gutman
Keyword(s):  
Molecular Structure ◽  
Standard Deviation ◽  
Structural Factor ◽  
Coupling Constants ◽  
Proton Proton ◽  
Vicinal Coupling Constants ◽  
Proton Coupling ◽  
Vicinal Proton ◽  
New Equation ◽  
Mutually Independent

Abstract A modification of the Karplus equation, containing four mutually independent structural terms and five adjustable parameters, is put forward. The new structural factor, introduced into this modification is sin (θ1 + θ2)/2. The new equation reproduces experimental NMR vicinal coupling constants of norbornenes with a standard deviation of about 0.45 Hz.

An 1H NMR conformational analysis of 3-phenylpentane in solution

1993 ◽  
Vol 71 (4) ◽  
pp. 520-525 ◽  
Author(s):  
Ted Schaefer ◽  
Lina B.-L. Lee
Keyword(s):  
Alkyl Chain ◽  
Chemical Shifts ◽  
Close Approach ◽  
Solvent Mixture ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Proton Proton ◽  
Vicinal Coupling Constants ◽  
Proton Coupling ◽  
Proton Chemical Shifts

Some 30 proton chemical shifts and proton–proton coupling constants are reported for a 4.7 mol% solution of 3-phenylpentane in a CS2/C6D12/TMS solvent mixture at 300 K. The long-range coupling constant over six formal bonds between the methine and para protons is used to deduce an apparent twofold barrier of 15.0 ± 0.3 kJ/mol to rotation about the Csp2—Csp3 bond, at least twice as large as that for isopropylbenzene in solution. AM1 computations agree with experiment in finding the conformation of lowest energy as that in which the methine C—H bond is situated in the phenyl plane, but predict a barrier height of only 13.9 kJ/mol. The vicinal coupling constants are consistent with a fractional population, 0.38(2), of the TT conformer, that in which all the carbon atoms of the alkyl chain lie in a plane. A doubly degenerate conformer, TG+(G−T), in which one methyl group is twisted away from the phenyl substituent, then has a fractional population of 0.62(2). The assumption that only these three conformers are present is tested with the signs and magnitudes of the four different coupling constants over four bonds. These coupling constants are consistent with the absence of significant proportions of the other six all-staggered conformers. These six are characterized by a close approach of the methyl groups (1,5 interactions) or by proximity of the methyl and phenyl moieties.

RELATIVE SIGNS OF GEMINAL AND VICINAL PROTON–PROTON COUPLING CONSTANTS IN α,β-DIPHENYLPROPIONIC ACID AND ITS METHYL ESTER

1962 ◽  
Vol 40 (8) ◽  
pp. 1483-1489 ◽  
Author(s):  
Robert R. Fraser
Keyword(s):  
Methyl Ester ◽  
Opposite Sign ◽  
Coupling Constants ◽  
Proton Proton ◽  
Vicinal Coupling Constants ◽  
Proton Coupling ◽  
Vicinal Proton

It has been shown that the geminal and vicinal coupling constants are of opposite sign in α,β-diphenylpropionic acid and its methyl ester. The significance of the results is discussed.

The Dependence of Vicinal Proton-Proton Coupling Constants on Molecular Structure

1994 ◽  
Vol 49 (7-8) ◽  
pp. 815-818
Author(s):  
Zoran Marković ◽  
Stanimir Konstantinović ◽  
Ivan Gutman
Keyword(s):  
Molecular Structure ◽  
Standard Deviation ◽  
Substituent Effect ◽  
Coupling Constants ◽  
Proton Proton ◽  
Vicinal Coupling Constants ◽  
Proton Coupling ◽  
Vicinal Proton ◽  
New Equation ◽  
Mutually Independent

Abstract A modification of the Karplus equation is put forward, containing for mutually independent structural terms and four adjustable parameters. Among the new factors introduced in this modifi­cation are the distance between protons and Muallay's group electronegativity, used in the evalua­tion of the α-substituent effect. The new equation reproduces experimental NMR vicinal coupling constants with a standard deviation of about 0.6 Hz.

21,22-Disubstituted 18α,19βH-Ursane Derivatives with Oxabicyclooctane System in Ring E

1993 ◽  
Vol 58 (1) ◽  
pp. 173-190 ◽  
Author(s):  
Eva Klinotová ◽  
Jiří Klinot ◽  
Václav Křeček ◽  
Miloš Buděšínský ◽  
Bohumil Máca
Keyword(s):  
Spectral Data ◽  
Spin Systems ◽  
Coupling Constants ◽  
Complete Analysis ◽  
Nmr Spectrum ◽  
Proton Proton ◽  
H Nmr ◽  
Proton Coupling ◽  
C Nmr

Reaction of 3β-acetoxy-21,22-dioxo-18α,19βH-ursan-28,20β-olide (IIIa) and 20β,28-epoxy-21,22-dioxo-19α,19βH-ursan-3β-yl acetate (IIIb) with diazomethane afforded derivatives XII-XIV with spiroepoxide group in position 21 or 22, which were further converted into hydroxy derivatives XV and XVII. Ethylene ketals VIII-X were also prepared. In connection with the determination of position and configuration of the functional groups at C(21) and C(22), the 1H and 13C NMR spectral data of the prepared compounds are discussed. Complete analysis of two four-spin systems in the 1H NMR spectrum of bisethylenedioxy derivative Xb led to the proton-proton coupling constants from which the structure with two 1,4-dioxane rings condensed with ring E, and their conformation, was derived.

Proton magnetic resonance study of the conformation of the pyrrolidine ring in some proline-thiohydantoins

1988 ◽  
Vol 53 (11) ◽  
pp. 2503-2510 ◽  
Author(s):  
Jef J. M. Sleeckx ◽  
Marc J. O. Anteunis ◽  
Frans A. M. Borremans
Keyword(s):  
Present Model ◽  
Coupling Constants ◽  
Proton Proton ◽  
Proton Coupling ◽  
Proton Magnetic Resonance Study ◽  
Vicinal Proton ◽  
Different Temperatures ◽  
Experimental Justification ◽  
State Assumption ◽  
Methyl Phenyl

The conformational behaviour of a series of N-substituted thiohydantoins of proline was studied by proton NMR. The pseudorotational parameters of the proline moiety were calculated from the ten vicinal proton-proton coupling constants assuming a two state equilibrium (N ⇋ S). The effect of the different substituents (methyl, phenyl, para-nitrophenyl) at the thiohydantoin nitrogen on the conformation of the pyrrolidine rings is discussed. The spectra of proline-N-methylthiohydantoin were recorded at different temperatures in octadeuterotoluene solution. The conformational analysis of these spectra showed that the ratio of the populations of the N and S forms changes considerably with temperature, while the conformational identity of both the N and S forms remains strictly preserved. These facts provide an additional experimental justification of the two-state assumption, at least so for the present model compounds.

High Pressure Studies of Quantum Well Emission and Deep Emission in GaInP(ordered)-GaAs Heterostructures

1997 ◽  
Vol 499 ◽  
Author(s):  
S. H. Kwok ◽  
P. Y. Yu ◽  
K. Uchida ◽  
T. Arai
Keyword(s):  
High Pressure ◽  
Quantum Well ◽  
Emission Band ◽  
Excitation Power ◽  
High Excitation ◽  
High Pressure Studies ◽  
Band Alignments ◽  
High Pressure Study

ABSTRACTWe report on a high pressure study of emission from a series of GaInP(ordered)/GaAs heterostructures. A so-called “deep emission” band at 1.46 eV is observed in all our samples. At high excitation power, quantum well emission emerges in only one structure where thin GaP layers are inserted on both sides of the GaAs well. From the pressure dependent emission in this sample we have determined its band alignments. The role of the GaP layers in suppressing the deep emission is elucidated.

Sign in / Sign up

Export Citation Format

Share Document