Strongly hindered rotation in α,α,2,6-terrachlorotoluene. Stereospecific five-bond coupling. Hyperconjugative contributions to long-range sidechain-ring proton coupling constants

1968 ◽  
Vol 46 (12) ◽  
pp. 2187-2188 ◽  
Author(s):  
T. Schaefer ◽  
R. Schwenk ◽  
C. J. Macdonald ◽  
W. F. Reynolds
Keyword(s):  
Free Energy ◽  
Resonance Spectrum ◽  
Coupling Constants ◽  
Proton Resonance ◽  
Kcal Mole ◽  
Hindered Rotation ◽  
Ring Proton ◽  
Meta Position ◽  
Proton Coupling ◽  
Free Energy Of Activation

At −40 °C the C—H bond of the dichloromethyl group of α,α,2,6-tetrachlorotoluene lies in the plane of the ring. The proton resonance spectrum demonstrates a stereospecific five-bond coupling between the C—H proton and the ring proton in the meta position. The coupling to the para proton is essentially zero as expected from a hyperconjugative mechanism. The free energy of activation of rotation of the dichloromethyl group is about 15 kcal/mole at 25 °C.

CORRELATIONS OF PROTON COUPLING CONSTANTS IN THE CYCLOPROPANE RING WITH ELECTRONEGATIVITY: CONSIDERATION OF THE PROTON RESONANCE SPECTRUM OF CYCLOPROPYLLITHIUM

1965 ◽  
Vol 43 (1) ◽  
pp. 75-80 ◽  
Author(s):  
T. Schaefer ◽  
F. Hruska ◽  
G. Kotowycz
Keyword(s):  
Resonance Spectrum ◽  
Cyclopropane Ring ◽  
Coupling Constants ◽  
Proton Spectrum ◽  
Proton Resonance ◽  
Individual Values ◽  
Proton Coupling

The analysis of cyclopropyllithium allows estimates to be made of all proton coupling constants. The exceptionally small couplings across carbon atoms 2 and 3 are examined in the context of correlations of coupling constants with the electronegativities of substituents. It is concluded that, although the couplings involving protons attached to the same carbon as the substituent decrease with increasing electronegativity of the substituent, the opposite is true for couplings involving the protons attached to carbons one bond removed from the substituent. Individual values are suggested for the coupling constants in cyclopropane itself and these agree with the observed I3C side bands in its proton spectrum.

Signs of long-range amino proton – ring proton coupling constants in N-ethyl-4-chloro-2-nitroaniline

1970 ◽  
Vol 48 (8) ◽  
pp. 1343-1345 ◽  
Author(s):  
T. Schaefer ◽  
R. Wasylishen
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Spin Coupling Constant ◽  
Proton Resonance ◽  
Ring Proton ◽  
Multiple Resonance ◽  
Proton Coupling ◽  
Spin Spin Coupling

In N-ethyl-4-chloro-2-nitroaniline there exists a measurable indirect spin–spin coupling constant of ±0.39 ± 0.03 Hz between the methylene protons and ring proton 6. The amino proton is coupled to ring protons 5 and 6 and also to the methylene protons. Consequently, although the amino proton resonance is broad due to incompletely relaxed coupling to 14N, normal multiple resonance experiments show that 5JmH,NH = 0.67 ± 0.03 Hz and 4JoH,NH = −0.35 ± 0.03 Hz.

SOLVENT EFFECTS AS AN AID IN THE ANALYSIS OF THE PROTON MAGNETIC RESONANCE SPECTRUM OF VINYL BROMIDE

1960 ◽  
Vol 38 (11) ◽  
pp. 2066-2073 ◽  
Author(s):  
T. Schaefer ◽  
W. G. Schneider
Keyword(s):  
Chemical Shift ◽  
Solvent Effects ◽  
Resonance Spectrum ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Vinyl Bromide ◽  
Proton Coupling ◽  
Geminal Proton ◽  
Geminal Coupling ◽  
Cis And Trans

By making use of specific solvent effects it has been possible to vary the relative chemical shift between the geminal protons of vinyl bromide from about +10 cycles/sec to −4 cycles/sec (at 60 Mc/sec) and to study the resultant changes in the proton resonance spectrum in the limiting region of zero chemical shift. Of particular interest is the growth and displacement of the combination lines, which appear in the resonance signals of the proton bonded to the same carbon atom as the bromine. From the variation of the six possible lines in this region it was confirmed that the cis and trans proton coupling constants must have the same sign. The intensity distribution of the lines in the geminal proton region require the geminal coupling constant to be of opposite sign to the other two.

Non-equivalence of vicinal proton–fluorine coupling constants in a CF3—CH2 group

1967 ◽  
Vol 45 (13) ◽  
pp. 1485-1489 ◽  
Author(s):  
Robert R. Fraser ◽  
Paul Hanbury
Keyword(s):  
Unique Feature ◽  
Resonance Spectrum ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Anomeric Effect ◽  
Proton Proton ◽  
Proton Coupling ◽  
Vicinal Proton ◽  
Different Temperatures ◽  
Tetrahydropyranyl Ether

The proton magnetic resonance spectrum of the tetrahydropyranyl ether of 2,2,2-trifluoroethanol has been measured in several solvents and at different temperatures. Analysis of the ABX3 pattern produced by the trifluoroethyl group revealed a unique feature. Under all conditions, it was found that the vicinal coupling constants JAX and JBX had different magnitudes. This non-equivalence is interpreted as evidence that the C—HA and C—HB bonds of the trifluoroethyl group differ electronically. A possible relation between this finding and the anomeric effect is discussed. In contrast to the above results, the tetrahydropyranyl ether of ethanol showed equal vicinal proton–proton coupling constants in the ethyl group.

A PROTON MAGNETIC RESONANCE INVESTIGATION OF ROTATIONAL ISOMERISM IN 1,1,2,2-TETRACHLORO-1-FLUOROETHANE

1961 ◽  
Vol 39 (1) ◽  
pp. 39-41 ◽  
Author(s):  
R. J. Abraham ◽  
H. J. Bernstein
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Rotational Isomerism ◽  
Coupling Constants ◽  
Proton Resonance ◽  
Resonance Investigation ◽  
Magnetic Resonance Investigation

The doublet separation in the proton resonance spectrum of the liquid was measured from −53 to 100 °C. From the variation of the separation with temperature approximate values of the trans and gauche HF coupling constants were obtained. The values of ΔH ≈ 400 cal/mole and ΔS ≈ 0 are also consistent with the data.

Temperature dependence of (+)-catechin pyran ring proton coupling constants as measured by NMR and modeled using GMMX search methodology

1997 ◽  
Vol 38 (6) ◽  
pp. 985-988 ◽  
Author(s):  
Fred L. Tobiason ◽  
Stephen S. Kelley ◽  
M.Mark Midland ◽  
Richard W. Hemingway
Keyword(s):  
Temperature Dependence ◽  
Coupling Constants ◽  
Pyran Ring ◽  
Ring Proton ◽  
Proton Coupling

Protonenresonanz-spektroskopische Untersuchungen am 1.2-Diphenyl-cyclobutadien-eisentricarbonyl. Ein Beitrag zur Kenntnis der Bindungsverhältnisse im komplex-gebundenen Cyclobutadien / The Proton Resonance Spectrum of 1,2-Diphenyl-cyclobutadiene-irontricarbonyl. An Investigation on Bonding Properties in Complex Stabilized Cyclobutadiene

1971 ◽  
Vol 26 (6) ◽  
pp. 570-576 ◽  
Author(s):  
Hans Albert Brune ◽  
Hans Hüther ◽  
Hans Hanebeck
Keyword(s):  
Resonance Spectrum ◽  
Membered Ring ◽  
Coupling Constants ◽  
Bond Orders ◽  
Proton Resonance ◽  
Carbon Carbon Bonds ◽  
Carbon Bonds ◽  
Bonding Properties ◽  
Single Bonds

The complete proton resonance spectrum of 1.2-diphenyl-cyclobutadiene-irontricarbonyl was measured including all observable 13C-H-coupling constants within the four-membered ring. The couplings were assigned. Their analysis excludes the structure of a rectangular cyclobutadiene with alternating double and single bonds; the carbon-carbon bonds of the four-membered ring have nearly uniform bond orders.

The proton magnetic resonance spectrum of triptycene. The effect of magnetic anisotropy on the proton shifts

1967 ◽  
Vol 45 (19) ◽  
pp. 2155-2162 ◽  
Author(s):  
K. G. Kidd ◽  
G. Kotowycz ◽  
T. Schaefer
Keyword(s):  
Current Model ◽  
Small Strain ◽  
Proton Magnetic Resonance Spectrum ◽  
Methine Proton ◽  
Coupling Constants ◽  
Proton Spectrum ◽  
Proton Proton ◽  
Ring Proton ◽  
Proton Shift ◽  
Proton Coupling

The ring proton spectrum of triptycene (2.2 mole % in CS2) was analyzed after the methine proton was decoupled. The modified ring current model accounts for most of the internal shift. Bond anisotropies and electron density contributions are also present. The latter account for the mean proton shift. The agreement between the predicted and calculated shifts is excellent for the proton meta to the methine substituent, but a discrepancy of 0.1 p.p.m. is found for the ortho proton. Correction for the ring anisotropy effects produces excellent agreement of the methine proton shift with the empirical correlation between the C—H proton shifts and the 13C–H coupling constants. The ring proton–proton coupling constants are little different from those in benzene, but a small strain in the bonds near the methine carbons is implied.

Solvent effects on the proton spectra of some halopropenes. The preparation and proton resonance spectra of the 1-iodopropenes

1967 ◽  
Vol 45 (10) ◽  
pp. 1081-1087 ◽  
Author(s):  
F. Hruska ◽  
D. W. McBride ◽  
T. Schaefer
Keyword(s):  
Hydrogen Bonding ◽  
Solvent Effects ◽  
Olefinic Proton ◽  
Coupling Constants ◽  
Proton Resonance ◽  
Methyl Proton ◽  
Reaction Field ◽  
Field Effects ◽  
Proton Coupling ◽  
Solvent Shifts

The preparation and proton resonance spectra of the 1-iodopropenes are reported and solvent effects on the proton spectra of the chloro-, bromo-, and iodo-compounds are measured. The proton coupling constants are discussed in terms of old and new electronegativity correlations. The olefinic cis and trans proton shifts can be attributed mainly to a paramagnetic contribution from the substituent, whereas the gem olefinic proton shifts depend in addition on the electron-withdrawing power of the substituent. The methyl proton shifts in the 1-substituted compound show little dependence on the substituent and this is discussed in relation to the barrier heights to methyl rotation. The solvent shifts in benzene cannot be completely reconciled with a dipole – induced dipole model. They increase with the size of the substituent and are largest for protons farthest from the substituent. The solvent shifts in acetone can be explained as due to weak hydrogen bonding and reaction field effects. The shifts of protons gem to the substituent arise mainly from hydrogen bonding, whereas the shifts of protons cis or trans have significant contributions from both effects. The reaction field effects can also account for the methyl shifts in acetone.

Nuclear magnetic resonance study of carbethoxypyrroles

1970 ◽  
Vol 48 (14) ◽  
pp. 2303-2305 ◽  
Author(s):  
M. W. Roomi ◽  
H. Dugas
Keyword(s):  
Chemical Shifts ◽  
Nuclear Magnetic Resonance Study ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Ring Proton ◽  
Proton Coupling ◽  
Low Field ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The chemical shifts and the ring proton coupling constants of various substituted carbethoxypyrroles are reported.The electron-withdrawing effect of the carbethoxy groups shifts the resonances of the ring substituents to low field while the inductive and mesomeric effects of the methyl groups shift the resonances to higher field. The deshielding effect is more pronounced with 2-carbethoxypyrroles than for 3-carbethoxypyrroles. The ring proton spin–spin coupling constants depend on the nature of substituents and increase with the electronegativity of the substituents. In some cases long-range coupling between the methyl side-chain protons and ring protons could be observed.

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