Hydrogen bonding and long-range proton coupling constants in some ortho disubstituted aniline derivatives. Intramolecular proton exchange and degree of nonplanarity of the amino group

1970 ◽  
Vol 48 (8) ◽  
pp. 1263-1268 ◽  
Author(s):  
R. Wasylishen ◽  
T. Schaefer
Keyword(s):  
Long Range ◽  
Proton Exchange ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Amino Group ◽  
Aniline Derivatives ◽  
Proton Coupling ◽  
Intramolecular Exchange ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Long-range spin–spin coupling constants over five bonds between the two amino protons and the ring protons are reported for some ortho disubstituted aniline derivatives in cyclohexane and benzene-d6 solutions. Equal coupling of both amino protons to the meta protons in unsymmetrically ortho disubstituted aniline derivatives indicates the occurrence of intramolecular exchange of the amino protons. The absence of any observable coupling over six bonds to the para proton places an upper limit on the degree of nonplanarity of the amino group in the 2,6-dibromo- and 2,6-dichloroanilines. A relatively basic compound like 2,4,6-trimethylaniline does not display long-range couplings of the amino protons, very likely because intermolecular proton exchange occurs.

Long-range spin–spin coupling constants between ring protons and aldehydic protons in some para-substituted benzaldehydes

1969 ◽  
Vol 47 (21) ◽  
pp. 4005-4010 ◽  
Author(s):  
S. S. Danyluk ◽  
C. L. Bell ◽  
T. Schaefer
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Proton Proton ◽  
Proton Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms ◽  
Benzaldehyde Derivatives

The long-range proton–proton coupling constants between the ring protons and the aldehydic proton are reported for a series of para-substituted benzaldehyde derivatives. It was found that JoH,CHO < 0 and JmH,CHO > 0. Furthermore, JoH,CHO increases in magnitude as the electron donating power of the sub-stituent increases. A similar trend is observed forJmH,CHO but the ratio of the increase to the magnitude of JmH,CHO is much less than for JoH,CHO. A good correlation is obtained between JoH,CHO and the sub-stituent parameters of Swain and Lupton.The coupling constant data are discussed in terms of σ and π coupling mechanisms and it is concluded that σ electron mechanisms are dominant for both JoH,CHO and JmH,CHO.

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.

The effects of substituents on the5J long-range spin-spin coupling constants in substituted benzaldehydes

1979 ◽  
Vol 12 (9) ◽  
pp. 542-543 ◽  
Author(s):  
R. H. Contreras ◽  
D. G. de Kowalewski ◽  
A. Osella
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Substituted Benzaldehydes ◽  
Spin Spin Coupling

Long-range spin–spin coupling constants as an indicator of conformational preferences in ethyl and trifluoroethyl vinyl ethers

1977 ◽  
Vol 55 (15) ◽  
pp. 2835-2838 ◽  
Author(s):  
Ted Schaefer ◽  
William J. E. Parr
Keyword(s):  
Vinyl Ether ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Ethyl Vinyl Ether ◽  
Spectroscopic Techniques ◽  
Ethyl Vinyl ◽  
Conformational Preferences ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The observed and calculated, negative, long-range spin–spin coupling constants over five bonds between olefinic and methylene protons in ethyl vinyl ether and in 2,2,2-trifluoroethyl vinyl ether are consistent with predominant s-cis planar conformations. The five-bond couplings are sensitive to the proximity of the bonds containing the coupled nuclei and are unobservably small in 1-butene where the H,H distances are somewhat larger than in the ethers. The present results concur with the arguments based on other spectroscopic techniques.

The Molecular Structure of Allenes and Ketenes, XIII Correlations of Carbon-Proton Spin-Spin Coupling Constants in Allenes with ab initio STO-3G Overlap Populations

1979 ◽  
Vol 34 (1) ◽  
pp. 118-120 ◽  
Author(s):  
Wolfgang Runge
Keyword(s):  
Molecular Structure ◽  
Ab Initio ◽  
Substituent Effects ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Proton Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Cl Atoms

Abstract It is shown that substituent effects on one-bond and long-range carbon-proton coupling constants in monosubstituted allenes parallel quantitatively ab initio STO-3G carbon 2s-hydrogen 1 s overlap populations, irrespectively of whether the substituents are bonded to the allenic skeleton via first-row (C, O) or second-row (Si, S, Cl) atoms.

Molecular orbital computations and 1H nuclear magnetic resonance measurements of the bending motion of xanthene in the gas and in solution

1990 ◽  
Vol 68 (9) ◽  
pp. 1548-1552 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Long Range ◽  
Solvent Mixture ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Ambient Temperatures ◽  
Folding Angle ◽  
Analytical Functions ◽  
Planar Molecule ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

STO-3G and 4-31G MO computations are reported for a range of values of the folding angle in xanthene, the dihedral angle between the benzene planes. Unlike 9,10-dihydroanthracene but like dibenzo-p-dioxin, its "parent" molecules, the inversion or puckering potential for xanthene is calculated to be rather flat. The molecular energies between a folding angle of 180° (planar molecule) and 120° are reproduced by analytical functions of [Formula: see text], θ being the folding angle. The long-range spin–spin coupling constants between the methylene protons and the aromatic protons at 300 K are reported for xanthene dissolved in a CS2/C6D12 solvent mixture and in acetone-d6 solution. These conformationally sensitive coupling constants are consistent with the theoretical puckering potentials and therefore with substantial "butterfly" motion at ambient temperatures. The computed geometries of xanthene are also given and briefly discussed. Keywords: xanthene, MO computations on inversion; xanthene, long-range spin–spin coupling constants; xanthene, internal motion; xanthene, inversion potentials.

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