Medium dependence of the proton chemical shift and H—H, H—F, F—F coupling constants in 1,1-difluoroethylene

1967 ◽  
Vol 45 (24) ◽  
pp. 3157-3164 ◽  
Author(s):  
C. J. Macdonald ◽  
T. Schaefer
Keyword(s):  
Chemical Shift ◽  
Dipole Moments ◽  
Coupling Constants ◽  
Proton Chemical Shift ◽  
Dispersion Interactions ◽  
Spectral Parameters ◽  
Proton Proton ◽  
Reaction Field ◽  
Solvent Dependence ◽  
Solvent Molecules

The solvent dependence of the proton chemical shift, the geminal proton–proton, the cis and trans proton–fluorine, and the geminal fluorine–fluorine coupling constants in 1,1-difluoroethylene is reported for 25 solvents. The shift and the couplings involving protons depend primarily on the dielectric constant of the medium, but the Onsager reaction field model is inadequate to describe the changes observed. The fluorine–fluorine coupling depends also on dispersion interactions with the solvent molecules. A comparison with the solvent behavior of the spectral parameters of vinyl fluoride, 1-chloro-1-fluoroethylene, and trifluoroethylene indicates the importance, in varying degrees, of reaction field effects, hydrogen bonding, dispersion interactions, the orientation of the solute dipole moments, and the polarizability of specific bonds in the solute molecule in determining their solvent-induced changes.

Solvents effects on the proton chemical shift and H—H, H—F coupling constants in 1-chloro-1-fluoroethylene. Reaction field and dispersion interactions

1967 ◽  
Vol 45 (10) ◽  
pp. 1111-1118 ◽  
Author(s):  
H. M. Hutton ◽  
T. Schaefer
Keyword(s):  
Dielectric Constant ◽  
Chemical Shift ◽  
Coupling Constants ◽  
Proton Chemical Shift ◽  
Coupling Constant ◽  
Dispersion Interactions ◽  
Proton Proton ◽  
Reaction Field ◽  
Proton Coupling ◽  
Solvent Molecules

The proton chemical shift and the geminal proton–proton and cis proton–fluorine coupling constants in 1-chloro-1-fluoroethylene depend primarily on the dielectric constant of the medium, although this dependence is not given by the Onsager reaction field model. A roughly linear relationship is found with the square root of the dielectric constant. The proton coupling constant decreases algebraically while the cis proton–fluorine coupling constant increases as the dielectric constant of the medium increases. The trans proton–fluorine coupling depends on dispersion interactions with the solvent molecules and increases as these interactions increase. The geminal coupling constant varies between − 3.8 and − 4.8 c.p.s., the cis coupling between 7.6 and 12.3 c.p.s., and the trans coupling between 36.9 and 38.6 c.p.s.

The conformational distribution of 2-cyanobenzaldehyde and 3-cyanobenzaldehyde in solution and in the vapor

1991 ◽  
Vol 69 (7) ◽  
pp. 1039-1046 ◽  
Author(s):  
Ted Schaefer ◽  
Kerry J. Cox ◽  
Rudy Sebastian
Keyword(s):  
Long Range ◽  
Dipole Moments ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Orbital Theory ◽  
Spectral Parameters ◽  
Proton Proton ◽  
H Nmr ◽  
Proton Coupling ◽  
Spin Spin Coupling

The 1H nuclear magnetic resonance spectra of 2-cyanobenzaldehyde (2CNB) and 3-cyanobenzaldehyde (3CNB) in CS2/C6D12 and acetone-d6 solutions at 300 K yield precise stereospecific long-range proton–proton coupling constants. These are used to establish the conformational population of the o-cis and o-trans conformers of these relatively polar molecules. For example, the fractional o-cis population of 2CNB changes from 0.12(4) in CS2/C6D12 to 0.46(6) in acetone-d6, whereas that of 3CNB is 0.48(2) in both solvents. Extrapolation to the vapor phase, using a dielectric model, implies a negligible concentration of the o-cis conformer of 2CNB and a roughly 50% abundance of each conformer of 3CNB. Computations at various levels of molecular orbital theory provide estimates of the rotational barrier of the aldehyde moiety and confirm the planar structure of each conformer. The geometries of three conformers are given as obtained from the 6-31G MO basis and may be useful to molecular spectroscopists. Theoretical and experimental dipole moments are interpolated to yield estimates of their magnitudes for the four planar conformers. Somewhat less precise 1H nmr spectral parameters (than for the above solutions) are also obtained for dilute solutions in benzene-d6 at 300 K. The conformational distributions based on these parameters are compared with their only other measurement, based on dipolar moments in benzene at 298 K. Good agreement between the results of the two methods is found for 3CNB but not for 2CNB. It is suggested that specific interactions occur between benzene solvent and solute molecules, particularly for 3CNB, for which these interactions stabilize the conformer having a low dipole moment. Remarkable changes in the intraring proton–proton coupling constants occur in going from CS2/C6D12 to acetone-d6 solution. Key words: 2- and 3-cyanobenzaldehyde (2CNB and 3CNB): 1H NMR, conformations, long-range spin–spin coupling constants, MO computations.

Internal motion in benzylidene diacetate and its 2,6-dibromo derivative by DNMR and the J method

1989 ◽  
Vol 67 (6) ◽  
pp. 1022-1026 ◽  
Author(s):  
Ted Schaefer ◽  
Craig S. Takeguchi
Keyword(s):  
Double Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Maximum Magnitude ◽  
Coupling Constant ◽  
Spectral Parameters ◽  
Proton Proton ◽  
Ether Solution ◽  
Spin Spin Coupling ◽  
Dibromo Derivative

The 1H nuclear magnetic resonance spectral parameters are reported for benzylidene diacetate in CS2 and acetone-d6 solutions. The long-range spin–spin coupling constant over six formal bonds, 6J, is used to derive apparent twofold barriers to rotation about the exocyclic C(1)—C bond in the two solutions. The conformation of lowest energy has the α. C—H bond in the benzene plane. The barrier is higher in CS2 than in acetone-d6 solution, in contrast to a molecule like benzyl chloride. In the 2,6-dibromo derivative, the free energy of activation for reorientation about the bond in question is 36 kJ/mol at 165 K in dimethyl ether solution. Such a high barrier implies a very small six-bond proton–proton coupling constant for this derivative because 6J is proportional to the expectation value of sin2θ. The angle θ is zero when the α C—H bond lies in the benzene plane. 6J is −0.051 Hz in acetone-d6 solutions; its sign is determined by double resonance experiments. The question of an angle-independent component of 6J, that is, whether 6J is finite at θ = 0°, is addressed. A maximum magnitude of 0.02 Hz may be present at θ = 0° for the 2,6-dibromo derivative, although a zero magnitude is also compatible with the experimental data. In a compound with a higher internal barrier, α,α,2,6-tetrachlorotoluene, the experimental results are best in accord with a negligibly small 6J at θ = 0°. Keywords: 1H NMR of benzylidene diacetate, spin–spin coupling constants for benzylidene diacetate, DNMR, 2,6-dibromobenzylidene diacetate.

scholarly journals Étude théorique de la structure du phosphate d'isaxonine

1984 ◽  
Vol 62 (4) ◽  
pp. 680-686
Author(s):  
Jean-Pierre Monti ◽  
Marcel Sarrazin ◽  
Pierre Brouant
Keyword(s):  
Chemical Shift ◽  
Molecular Orbital ◽  
Coupling Constants ◽  
Published Data ◽  
Molecular Orbital Calculations ◽  
Good Prediction ◽  
Proton Chemical Shift ◽  
Screening Constant ◽  
Bond Lengths ◽  
Bond Indices

Protonations of isaxonine phosphate are studied by performing CNDO/2 and CNDO/S molecular orbital calculations. Results are compared with previously published data. Wiberg's bond indices and S character percentages calculated using electronic populations are shown to correctly predict variations of bond lengths and bond angles as well as [Formula: see text] coupling constants. A good prediction of proton chemical shift variations using a calculation of the screening constant was obtained.

Concerning the role of the reaction field in the proton shielding of molecules in solution

1967 ◽  
Vol 45 (10) ◽  
pp. 1093-1096 ◽  
Author(s):  
G. Kotowycz ◽  
T. Schaefer
Keyword(s):  
Dielectric Constant ◽  
Chemical Shift ◽  
Solute Molecule ◽  
Proton Chemical Shift ◽  
Square Root ◽  
Reaction Field ◽  
Strong Curvature

It is shown that the strong curvature in some plots of proton chemical shift σ versus the Onsager reaction field E can be removed by plotting the shifts of the solute molecule versus the square root of the dielectric constant of the medium. The resulting values of k in the equation σ = −kE cos θ are fairly consistent and reasonable in magnitude.

The Anisotropic Polarizability of a few Aromatic Hydrocarbons

1972 ◽  
Vol 27 (8-9) ◽  
pp. 1336-1344 ◽  
Author(s):  
W. Liptay ◽  
H.-J. Schlosser
Keyword(s):  
Dipole Moment ◽  
Electric Dipole Moment ◽  
Electric Dipole ◽  
Polarizability Tensor ◽  
Reaction Field ◽  
Permanent Electric Dipole Moment ◽  
Solvent Dependence ◽  
Solvent Molecules ◽  
Kerr Constants ◽  
Electronic Ground

Abstract For sufficiently symmetric molecules without a permanent electric dipole moment, it is shown that refractive indices, Kerr constants and electrooptical absorption measurements in suitable non-polar solvents can be utilized to determine the components αcgx, αgy, αgz of the polarizability tensor of solute molecules in the electronic ground state. Since the required quantities are avail-able for anthracene, tetracene, perylene and bianthryl, an evaluation of the polarizability tensor components is made possible.In solutions where the solvent molecules possess a permanent electric dipole moment or a sufficiently large quadrupole moment, as for example benzene, the fluctuations of the reaction field cause a contribution to the Kerr constant which may be an essential reason for its solvent dependence.

Tritium labelling and tritium N.M.R. II. Labelled methyl (Z)-Octadec-9-enoate obtained by partial hydrogenation on Lindlar catalyst, and its reduction to(Z)-Octadec-9-en-1-ol

1982 ◽  
Vol 35 (8) ◽  
pp. 1615 ◽  
Author(s):  
AL Odell ◽  
KJ Ronaldson ◽  
RW Martin ◽  
DJ Calvert
Keyword(s):  
Chemical Shift ◽  
Finite Difference ◽  
Isotope Effect ◽  
Coupling Constants ◽  
Partial Hydrogenation ◽  
Double Bonds ◽  
Proton Proton ◽  
Proton Coupling ◽  
Lindlar Catalyst

The selectivity of tritium labelling of double bonds by partial hydrogenation of the acetylenic analogue on Lindlar catalyst is investigated by 3H and 13C n.m.r. Examples of both the secondary isotope effect on chemical shift and the usefulness of 3H n.m.r, measurements to calculate proton-proton coupling constants are described. In the absence of proton coupling a finite difference (0.014 ppm) in the chemical shift of tritons at positions 9 and 10 of methyl (Z)-[9,10-3H]octadec-9-enoate is observed.

Dipole Moments, Polarizabilities and the Fluorescence Behaviour of 4-(9-anthryl)-N,N-dimethylaniline

1979 ◽  
Vol 34 (9) ◽  
pp. 1070-1082 ◽  
Author(s):  
Wolfram Baumann ◽  
F. Petzke ◽  
K.-D. Loosen
Keyword(s):  
Electric Field ◽  
External Electric Field ◽  
Decay Time ◽  
Fluorescence Spectra ◽  
Dipole Moments ◽  
Absorption And Fluorescence Spectra ◽  
Dependent Effect ◽  
Reaction Field ◽  
Solvent Dependence

Abstract It is shown that the solvent dependence of the fluorescence wavenumber and decay time as well as the solvent dependent effect of an external electric field on the absorption and fluorescence spectra of 4-(9-anthryl)-N,N-dimethylaniline can be fully understood taking into account reaction field induced polarizability effects.

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