Spin–spin coupling between hydroxyl and aldehydic protons in some salicylaldehyde derivatives. Correlation with the hydroxyl proton chemical shift

1984 ◽  
Vol 62 (2) ◽  
pp. 326-331 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Reino Laatikainen ◽  
Salman R. Salman
Keyword(s):  
Chemical Shift ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Mechanism ◽  
Spectral Parameters ◽  
Hydroxyl Proton ◽  
H Nmr ◽  
Group A ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

1H nmr spectral parameters are reported for salicylaldehyde and 15 of its derivatives in dilute CCl4 solutions. In those compounds in which sufficiently large substituents are placed ortho to either of the functional groups or in which substituents enhance the charge density in the carbonyl group, a positive spin–spin coupling is observed between the two sidechain protons. This coupling, formally over five bonds, correlates with the chemical shift of the hydroxyl proton. The coupling mechanism is discussed from various viewpoints. STO 3G MO calculations give an optimized planar structure for salicylaldehyde. Nonplanar structures are less stable than the planar form. The energy of the hydrogen bond in salicylaldehyde lies near 30 kJ/mol and increases to 36 kJ/mol in the 4,6-dimethoxy derivative. Other small long-range spin–spin coupling constants in these compounds are also discussed.

The planar conformation of 2-methylthiobenzaldehyde in solution

1983 ◽  
Vol 61 (1) ◽  
pp. 26-28
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spectral Parameters ◽  
H Nmr ◽  
Heavy Atoms ◽  
Planar Conformation ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Infrared Data

The 1H nmr spectral parameters are extracted for a 4 mol% solution of 2-methylthiobenzaldehyde in CCl4 at 305 K. The long-range spin–spin coupling constants involving the aldehydic and methyl protons are consistent only with a preferred conformation in which all heavy atoms are coplanar, as are the chemical shifts of the ring and methyl protons. This conclusion contradicts previous interpretations of the dipole moment, the nmr parameters, and of the infrared data for CCl4 solutions. The present data show that the O-syn and O-anti forms of the compound are present in roughly equal proportions.

Weiss's endo- and exo-tetracyclo[5.5.1.0.2,6 010,13]tridecane-4,8,12-trione: analysis of 1H NMR couplings in a system of fused 5-membered rings

1994 ◽  
Vol 72 (9) ◽  
pp. 1926-1932 ◽  
Author(s):  
Steven H. Bertz ◽  
Weijiang Zhang ◽  
James M. Cook ◽  
Martha D. Bruch ◽  
Lynn W. Jelinski
Keyword(s):  
Spin Systems ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Theoretical Treatment ◽  
H Nmr ◽  
Tightly Coupled ◽  
Nmr Techniques ◽  
Spin Coupling Constants ◽  
Stringent Test ◽  
Spin Spin Coupling

The configurational isomers of the title compounds consist of four fused five-membered rings. They contain tightly coupled 1H NMR spin systems, which provide excellent models for establishing the relationships between coupling constants and conformation. Complete chemical shift assignments and spin–spin coupling constants are reported for the title compounds by using high-field (500 MHz) 1H NMR techniques (e.g., 2D homonuclear and heteronuclear experiments, difference NOE enhancements, and computational spin simulations). In addition to the more familiar two- and three-bond couplings, the spectra of 1 and 2 also contain a number of long-range (four- and five- bond) couplings, which provide a stringent test of Barfield's theoretical treatment of four-bond couplings.

Analysis of the proton and fluorine magnetic resonance spectra of 1,3,5-trifluorobenzene dissolved in a nematic liquid crystal

1968 ◽  
Vol 46 (17) ◽  
pp. 2783-2786 ◽  
Author(s):  
C. T. Yim ◽  
D. F. R. Gilson
Keyword(s):  
Liquid Crystal ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Nematic Liquid Crystal ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
The Absolute ◽  
Spin Spin Coupling ◽  
Magnetic Resonance Spectra

The proton and fluorine magnetic resonance spectra of 1,3,5-trifluorobenzene oriented in a nematic liquid crystal have been analyzed. The proton and fluorine chemical shift anisotropies are −2.98 p.p.m. and 104 p.p.m. respectively. The absolute signs of the indirect spin–spin coupling constants are: JHH′, JFF, and JHF (ortho) all positive, and [Formula: see text] (para) negative.

Information from stereospecific spin–spin couplings about the relative absorptivities of the hydroxyl stretching bands in 2-iodophenol solutions

1981 ◽  
Vol 59 (21) ◽  
pp. 3021-3025 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Timothy A. Wildman
Keyword(s):  
Free Energy ◽  
Molecular Orbital ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Temperature Dependent ◽  
Hydroxyl Proton ◽  
Spin Coupling Constants ◽  
Cis And Trans ◽  
Spin Spin Coupling

The stereospecific spin–spin coupling constants between the hydroxyl proton and the ring protons for 2-iodophenol in various solvents yield some free energy differences between the cis and trans conformations of this molecule at 305 K. Comparison with areas of the hydroxyl stretching bands in the same or similar solvents shows that the ratio of the absorptivity coefficients for the two conformers is sensitive to solvent. It is suggested that this ratio is temperature dependent and therefore apparent enthalpy differences must be considered tentative for at least some solutions. Molecular orbital calculations are consistent with the arguments concerning the absorptivity coefficients.

Spin–spin coupling constants between side-chain and ring fluorine nuclei in some benzotrifluoride, benzal fluoride, and benzyl fluoride derivatives: coupling mechanisms

1979 ◽  
Vol 57 (7) ◽  
pp. 807-812 ◽  
Author(s):  
Ted Schaefer ◽  
Walter Niemczura ◽  
Chiu-Ming Wong ◽  
Kirk Marat
Keyword(s):  
Nmr Spectra ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Complete Analysis ◽  
Side Chain ◽  
Coupling Mechanism ◽  
Conformational Preferences ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms

A complete analysis of the 1H and 19F nmr spectra of 2,5- and 3,4-difluorobenzotrifluoride, together with multiple resonance experiments, yields the signs and magnitudes of the long-range 19F,19F and 1H,19F spin–spin coupling constants. The coupling mechanisms are discussed. In particular, the coupling over six bonds, [Formula: see text], whose sign is interpretable in terms of a σ–π mechanism, is too large in magnitude when compared to [Formula: see text], and [Formula: see text] in the analogous compounds. These latter three couplings are consistent in sign and magnitude with what is known about hyperfine interaction constants. The magnitudes of [Formula: see text] are reported for 4-fluorobenzotrifluoride, 3-amino-4-fluorobenzotrifluoride, 3-nitro-4-fluorobenzotrifluoride, as are 6JpF,F values for p-fluorobenzal fluoride and p-fluorobenzyl fluoride. In contrast to 6JpH,CH and 6JpF,CH it seems unlikely that, unless its coupling mechanism becomes more precisely understood, 6JpF,CF will be a reliable indicator of conformational preferences.

Spin–spin coupling constants as indicators of the conformation of anthrone in solution

1982 ◽  
Vol 60 (17) ◽  
pp. 2274-2277 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Timothy A. Wildman ◽  
Heather Dettman
Keyword(s):  
Nmr Spectra ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Central Ring ◽  
H Nmr ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The analyses of the 1H nmr spectra of fluorene, 2,7-dibromofluorene, and anthrone are reported. The benzylic couplings in these compounds are compared with those in indene and toluene. It is argued that the six-bond and five-bond couplings in anthrone are more compatible with a nonplanar than a planar central ring. The spectrum of the 2,7-dibromofluorene suggest that couplings between protons in different benzenoid rings are small, perhaps no larger than 0.05 Hz.

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.

Proton Magnetic Resonance Study of Intramolecular Hydrogen Bonding in Halophenols

1974 ◽  
Vol 52 (17) ◽  
pp. 3037-3041 ◽  
Author(s):  
J. Brian Rowbotham ◽  
T. Schaefer
Keyword(s):  
Intramolecular Hydrogen Bonding ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Magnetic Resonance Study ◽  
Hydroxyl Proton ◽  
Hydrogen Bond Strength ◽  
Proton Magnetic Resonance Study ◽  
Spin Coupling Constants ◽  
Intramolecular Hydrogen ◽  
Spin Spin Coupling

The long-range spin–spin coupling constants over five bonds between the hydroxyl proton and the ring protons in a series of trihalophenols imply that the intramolecular hydrogen bond strength (negative enthalpy) to fluorine is greater than that to iodine by 75 ± 20 cal/mol, whereas the strengths to chlorine and bromine are 460 ± 60 cal/mol greater than to iodine. If a distinction can be made between chlorine and bromine, then chlorine–hydrogen bonds more strongly by only a few tens of calories per mol. The measurements were made mainly on dilute solutions in carbon tetrachloride at 32 °C.

DFT calculations of 31P spin-spin coupling constants and chemical shift in dioxaphosphorinanes

2011 ◽  
Vol 49 (7) ◽  
pp. 399-404 ◽  
Author(s):  
Magdalena Pecul ◽  
Mateusz Urbańczyk ◽  
Artur Wodyński ◽  
Michał Jaszuński
Keyword(s):  
Chemical Shift ◽  
Dft Calculations ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling
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