1H nuclear magnetic resonance and molecular orbital estimates of the internal rotational barrier in phenylpropynal in solution and in the vapor

1992 ◽  
Vol 70 (9) ◽  
pp. 2365-2369 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Robert W. Schurko
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Molecular Orbital ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Basis Sets ◽  
Am1 Calculations ◽  
Internal Barrier ◽  
The One ◽  
Nuclear Magnetic

The 1H nuclear magnetic resonance spectra of phenylpropynal and 1-phenylpropyne are analyzed for CS2/C6D12 and acetone-d6 solutions. The ensuing spin–spin coupling constants over eight formal bonds are used in assessing the conformational dependence of the one in the propynal derivative, as compared to the one over six bonds in benzaldehyde. The eight-bond coupling constant in phenylpropynal implies, via a hindered rotor model, that the twofold barrier to internal rotation is 5.9 ± 1.6 kJ/mol in both solutions. This number is much smaller than that for the internal barrier in benzaldehyde, reflecting the reduced π electron conjugation in phenylpropynal. Molecular orbital computations, with geometry optimization, confirm the essentially purely twofold internal barrier in the free propynal. The theoretical magnitudes are given for AM1 calculations, as well as for abinitio computations with STO-3G, 3-21G, 6-31G, and 6-31G* bases. To within experimental error, the barrier magnitudes from the split-valence basis sets agree with those obtained in solution.

1H nuclear magnetic resonance and molecular orbital studies of the structure and internal rotations in ethylbenzene

1987 ◽  
Vol 65 (4) ◽  
pp. 873-877 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner ◽  
Rudy Sebastian
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Molecular Orbital ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Orbital Theory ◽  
Spectral Parameters ◽  
Internal Barrier ◽  
Nuclear Magnetic

Rather extensive geometry-optimized computations at the STO-3G, 4-21G, 4-31G, and 6-31G levels of abinitio molecular orbital theory suggest that the fourfold component of the barrier to internal rotation about the Csp2—Csp3 bond in ethylbenzene amounts to about 20% of the twofold component. The 1H nuclear magnetic resonance spectral parameters, extracted by complete analyses of the spectra arising from the ten protons, are reported for ethylbenzene in acetone-d6, CCl4, CS2, and perfluoromethylcyclohexane solutions. The long-range proton–proton spin–spin coupling constants demonstrate that the internal barrier is insensitive to the polarity of the solvent, in contrast to polar solute molecules such as benzyl fluoride. The coupling constants do not support a dependence of the internal barrier on the internal pressure of the solvent.

1H, 19F, and 13C nuclear magnetic resonance approaches to the barrier to rotation about the Csp2—Csp3 bond in 1,1,1 -trifluoro-2-phenylethane. Proximate coupling constants and molecular orbital computations

1995 ◽  
Vol 73 (9) ◽  
pp. 1387-1394 ◽  
Author(s):  
Ted Schaefer ◽  
Paul Hazendonk ◽  
David M. McKinnon
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Molecular Orbital ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
13C Nuclear Magnetic Resonance ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Nuclear Magnetic

The 1H, 19Fand 13C{1H} nuclear magnetic resonance spectra of 1,1,1-trifluoro-2-phenylethane, 1, in CS2–C6D12, acetone-d6, and benzene-d6 solutions, on analysis, yield long-range coupling constants from which are derived the apparent twofold barriers to rotation about the Csp2—Csp3 bonds. The twofold barrier is 9.0(2) kJ/mol, independent of solvent, 4.0 kJ/mol larger than that of ethylbenzene, also independent of solvent. The theoretical barrier heights for the free molecules at the post-Hartree–Fock level of molecular orbital theory (frozen-core MP2/6-31G*) also differ by 4 kJ/mol, but are about 1 kJ/mol higher than the experimental estimates. The perpendicular conformer is the most stable for both molecules. Comparisons are made with the benzyl halides, in which the internal barriers are remarkably sensitive to solvent. A spin–spin coupling constant over five formal bonds, 5J(H, F), involving the ortho protons in 1, is +0.74(2) Hz and is discussed in some detail in terms of its dependence on intenuclear distances (possible through-space interactions). The solvent perturbations of 3J(H, F) and of 2J(C, F) are of opposite sign. Other long-range coupling constants or their absence are also pointed out. For example, those between 19F and 13C nuclei or protons at the meta position are effectively zero; at the para position they are significant. Keywords: 1,1,1-trifluoro-2-phenylethane; 1H, 19F, and 13C NMR; long-range spin-spin coupling constants; through-space 1H, 19F spin–spin coupling constants; internal rotational potential; molecular orbital computations of internal potential.

PREFERRED RESIDENCE CONFORMATIONS OF DIASTEREOISOMERIC α–β AMINO ALCOHOLS: AN N.M.R. STUDY OF THE EPHEDRINES

1961 ◽  
Vol 39 (12) ◽  
pp. 2536-2542 ◽  
Author(s):  
J. B. Hyne
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Hydrogen Bonding ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Amino Alcohols ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Nuclear Magnetic

Nuclear magnetic resonance spectral results including chemical shifts, anisotropy effects, spin coupling constants, and hydrogen bonding phenomena are presented for the diastereoisomeric pair of α–β amino alcohols (−)-ephedrine and (+)-Ψ-ephedrine. The results are shown to be in keeping with the existence of a preferred residence conformation for each of the diastereoisomers.

Carbon-13 nuclear magnetic resonance studies of (Z)-5-fluoro-2-methyl-1-{[p-(methylsulfinyl)phenyl] methylene}-1H-indene-3-acetic acid (sulindac) and some related compounds

1978 ◽  
Vol 56 (16) ◽  
pp. 2129-2133 ◽  
Author(s):  
Alan Wilmot Douglas
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Acetic Acid ◽  
Magnetic Resonance ◽  
Nuclear Spin ◽  
Substituent Effects ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nuclear Magnetic Resonance Spectra ◽  
Spin Coupling Constants ◽  
Nuclear Magnetic

Carbon-13 nuclear magnetic resonance spectra have been obtained and fully assignee for a number of 2-methyl-1-{[p-(methylthio) or -(methylsulfinyl}phenyl]methylene}-1H-indene-3- acetic acid derivatives, including the potent anti-inflammatory compound sulindac, 1Z. Paired E and Z isomers were studied along with the sulindac sodium salt and ethyl ester in the Z series. Variations in steric crowding in E vs. Z isomers produce chemical shift effects which alternate with the number of intervening bonds. Fluorine substituent effects and 19F nuclear spin coupling to 13C nuclei, second-order features in off-resonance proton-decoupled spectra, and values of long-range 13CH nuclear spin coupling constants have been employed in making a complete set of assignments.

Nuclear magnetic resonance of some fluoro-substituted phenyl and benzyl mercurials

1968 ◽  
Vol 21 (10) ◽  
pp. 2411 ◽  
Author(s):  
W Kitching ◽  
W Adcock ◽  
BF Hegarty
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nuclear Magnetic Resonance Data ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Electronic Effects ◽  
Magnetic Resonance Data ◽  
Resonance Data ◽  
Spin Coupling Constants ◽  
Nuclear Magnetic

l9F and lH nuclear magnetic resonance data are reported for the para and meta fluoro-phenyl and -benzyl mercurials of types R2Hg and RHgX where X is a halide. The 19F data for the fluorophenyl mercurials provide no evidence for direct aryl-mercury conjugation, and mercuri substituents exert very feeble electronic effects. The shielding for the fluorobenzyl mercurials suggests a quite pronounced o-p electron donating effect for the metallomethyl group (NCH2-). Some 199Hg-lH spin coupling constants are derived from the proton spectra of the benzyl mercurials.

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