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.

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.

Investigation of Factors Affecting Conformational Preference in Complex Haloethane Derivatives by Classical Energy Calculations

1973 ◽  
Vol 51 (16) ◽  
pp. 2659-2670 ◽  
Author(s):  
William F. Reynolds ◽  
Donald J. Wood
Keyword(s):  
Solvation Energy ◽  
Coupling Constants ◽  
Conformational Preference ◽  
Factors Affecting ◽  
Energy Calculations ◽  
Vicinal Coupling Constants ◽  
Classical Energy ◽  
Dipole Interactions ◽  
Related Compounds ◽  
Good Agreement

Classical energy calculations are used in combination with Abraham's electrostatic theory of solvation energy to estimate rotamer energy differences for haloethane derivatives. The calculations are tested by comparing experimental and calculated ΔE values for several di- and tetrahaloethanes. There is good agreement for chloro and bromo derivatives but poorer agreement for fluoro and iodo derivatives. ΔE values in solution are also estimated for l4 complex chloro- and bromoethanes which we have previously investigated by n.m.r. spectroscopy. The calculations generally parallel the experimental results as reflected by vicinal coupling constants. They are particularly useful for trends in conformational preference for closely related compounds and are used in conjunction with vicinal coupling constants to identify diastereomers produced by halogenation of alkenes. Steric interactions, dipole–dipole interactions and solvation energy are all important in determining conformational preference for complex haloethanes in solution.

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.

Darstellung und Kristallstruktur von endo-2-Dimethylphospliono-exo-2-liydroxy-(—)-camphan zur Bestimmung von 3J(CCCP)-Vicinalkopplungen / Synthesis and Crystal Structure of endo-2-Dimethylphosphono-exo-2-hydroxy-(—)-camphane for the Determination of 3J(CCCP) Vicinal Coupling Constants

1979 ◽  
Vol 34 (11) ◽  
pp. 1547-1551 ◽  
Author(s):  
Gunadi Adiwidjaja ◽  
Bernd Meyer ◽  
Joachim Thiem
Keyword(s):  
Coupling Constants ◽  
Coupling Constant ◽  
Nmr Spectrum ◽  
Synthesis And Crystal Structure ◽  
X Ray ◽  
Vicinal Coupling Constants ◽  
Complete Assignment ◽  
Hydroxy Phosphonates ◽  
C Nmr

endo-2-Dimethylphosphono-exo-2-hydroxy-(-)-camphane (2) is prepared and the structure confirmed by X-ray data. The complete assignment of the 13C NMR spectrum of this conformationally rigid derivative leads to a Karplus-type function for the vicinal 3J(CCCP) coupling constant in α-hydroxy phosphonates.

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.

The effect of substituents on geminal proton–proton coupling constants. III

1977 ◽  
Vol 55 (14) ◽  
pp. 2642-2648 ◽  
Author(s):  
Roger N. Renaud ◽  
John W. Bovenkamp ◽  
Robert R. Fraser ◽  
Raj Capoor
Keyword(s):  
Coupling Constants ◽  
Coupling Constant ◽  
Mo Calculations ◽  
Proton Proton ◽  
Effect Of Substituents ◽  
Proton Coupling ◽  
Geminal Proton ◽  
Geminal Coupling ◽  
The Difference ◽  
Methylene Group

The effect of substituents at the 3-position in a series of N-methyl 5,6-dihydro-7H,12H-di-benzo[c,f]azocines on the geminal coupling constants of the C-12 methylene protons has been determined. The slope of the Hammett plot of 2J vs. σ has been found to be +0.20. The orientation of the methylene protons with respect to the π orbitals of the benzene ring bearing the substituent is such that no hyperconjugative effect should be present. The value of +0.20 is in contrast to a previously measured slope of −1.9 for compounds having a geometry ideal for hyperconjugative effects and substantiates the predictions of theoretical MO calculations. As a result, the reliability of this conformational dependence of ρ for use in conformational analysis has been strengthened.A comparison of the data for the azocines with those in the literature indicates the difference between the minimum and maximum effects of a phenyl substituent on a geminal coupling constant of an attached methylene group is 5.5 Hz.

Dihedral Angular Dependence of H—N—C—H Coupling Constants. Protonated Amines in Trifluoroacetic Acid

1973 ◽  
Vol 51 (15) ◽  
pp. 2433-2437 ◽  
Author(s):  
Robert R. Fraser ◽  
Roger N. Renaud ◽  
John K. Saunders ◽  
Yuk Y. Wigfield
Keyword(s):  
Angular Dependence ◽  
Trifluoroacetic Acid ◽  
Coupling Constants ◽  
Tertiary Amines ◽  
Coupling Constant ◽  
Vicinal Coupling Constants ◽  
Protonated Amines

Measurements of vicinal H—N—C—H coupling constants in the conjugate acids of two tertiary amines having known rigid conformations provide support for the validity of the Karplus relation for this type of coupling constant. Seven vicinal coupling constants agree to within 0.5 Hz with those calculated from the expression [Formula: see text].

Effect of Solvent Upon the Vicinal Proton Coupling Constants of Complex Substituted Ethanes. III. 1,2-Dihaloalkanes

1971 ◽  
Vol 49 (21) ◽  
pp. 3438-3442 ◽  
Author(s):  
D. A. Dawson ◽  
W. F. Reynolds
Keyword(s):  
Long Range ◽  
Conformational Changes ◽  
Coupling Constants ◽  
Effect Of Solvent ◽  
Vicinal Coupling Constants ◽  
Proton Coupling ◽  
Vicinal Proton ◽  
The Difference

The n.m.r. spectra of eight 1,2-dihaloalkanes have been determined in solvents of differing polarity. The relative rotamer stabilities for each compound have been deduced from the variation of the difference and sum of vicinal coupling constants with solvent. Variations in geminal and long range coupling constants with solvent are also attributed to conformational changes.

Assessing the Calculation of Exchange Coupling Constants and Spin Crossover Gaps Using the Approximate Projection Model to Improve Density Function Calculations

2019 ◽  
Author(s):  
Xianghai Sheng ◽  
Lee Thompson ◽  
Hrant Hratchian
Keyword(s):  
Density Functional Theory ◽  
Exchange Coupling ◽  
Density Functional ◽  
Spin Crossover ◽  
Coupling Constants ◽  
Spin Projection ◽  
Coupling Constant ◽  
Projection Model ◽  
Functional Theory

This work evaluates the quality of exchange coupling constant and spin crossover gap calculations using density functional theory corrected by the Approximate Projection model. Results show that improvements using the Approximate Projection model range from modest to significant. This study demonstrates that, at least for the class of systems examined here, spin-projection generally improves the quality of density functional theory calculations of J-coupling constants and spin crossover gaps. Furthermore, it is shown that spin-projection can be important for both geometry optimization and energy evaluations. The Approximate Project model provides an affordable and practical approach for effectively correcting spin-contamination errors in molecular exchange coupling constant and spin crossover gap calculations.

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