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.

Effect of Solvent Upon the Vicinal Proton Coupling Constants of Complex Substituted Ethanes. II. Anomalous Results for 1-Phenyl-1,2,2-trihaloethanes

1971 ◽  
Vol 49 (8) ◽  
pp. 1209-1217 ◽  
Author(s):  
W. F. Reynolds ◽  
D. J. Wood
Keyword(s):  
Hydrogen Bonding ◽  
Solvent Effects ◽  
Coupling Constants ◽  
Electrostatic Model ◽  
Effect Of Solvent ◽  
Vicinal Coupling Constants ◽  
Proton Coupling ◽  
General Terms ◽  
Vicinal Proton

The n.m.r. spectra of 11 tetra-substituted ethanes have been obtained in a number of solvents. Changes in the vicinal coupling constants of 1-phenyl-1,2,2-trihaloethanes with solvent do not fit the electrostatic model for solvent effects. It is concluded that the theory breaks down because solute–solvent hydrogen bonding specifically favors the trans rotamers of these compounds. The conditions under which the theory would be expected to break down are also discussed in more general terms.

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.

Concerning a relationship between long-range ring proton – methyl proton coupling constants and mobile bond order

1968 ◽  
Vol 46 (4) ◽  
pp. 654-656 ◽  
Author(s):  
D. J. Blears ◽  
S. S. Danyluk ◽  
T. Schaefer
Keyword(s):  
Linear Relationship ◽  
Long Range ◽  
Bond Order ◽  
Coupling Constants ◽  
Methyl Proton ◽  
Methyl Group ◽  
Potential Barriers ◽  
Proton Coupling ◽  
Induced Changes ◽  
Excitation Parameters

Long-range proton – methyl proton coupling constants in propene, mesitylene, 9-methylphenanthrene, and acenaphthene appear to be linearly related to the square of the mobile bond order between the carbon atoms bonded to the methyl group and the proton. However, substituent-induced changes in the charge on and hybridization state of the carbon atoms, in excitation parameters and in potential barriers to rotation of the methyl group, may also affect the coupling. Such changes must be considered in the application of a possible linear relationship.

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.

Sporidesmins. XV, The 13C nuclear magnetic resonance spectra of sporidesmin and sporidesmin-D. The evidence in the spectra for strain imposed by an epidithio bridge

1976 ◽  
Vol 29 (10) ◽  
pp. 2307 ◽  
Author(s):  
JW Ronaldson
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Coupling Constants ◽  
Carbonyl Groups ◽  
Proton Resonance ◽  
Methyl Proton ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
Electro Negativity ◽  
Magnetic Resonance Spectra

The proton-noise-decoupled 13C N.M.R. spectra of sporidesmin and sporidesmin-D are presented. The detailed assignments were worked out from the undecoupled spectrum of sporidesmin-D. The 3-methyl resonance moved downfield (by 7.3 ppm) upon cleavage of the -S-S- bridge in sporidesmin while the peaks of the two quaternary carbons to which the sulphurs are bound moved upfield (by 4.7 ppm). Lactam N-methyl and indoline N-methyl proton resonance decoupling showed that their p.m.r. assignments should be reversed. The electro-negativity of nitrogen, sulphur and carbonyl groups increased the coupling constants of the 3-CH3 by 7Hz and of the 11-CH by 10 Hz. The carbon of the lactam N-methyl was shielded by 14 ppm. There were six three-bond couplings, four HCN13C and two HCO13C, evident but no non-aromatic HCC13C couplings.

Anharmonicity, solvent effects, and hydrogen bonding: NH stretching vibrations

1970 ◽  
Vol 48 (14) ◽  
pp. 2197-2203 ◽  
Author(s):  
A. Foldes ◽  
C. Sandorfy
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Solvent Effects ◽  
Bond Formation ◽  
Hydrogen Bond Formation ◽  
Stretching Vibration ◽  
Solvent Shifts ◽  
Stretching Vibrations ◽  
Secondary Amides ◽  
Influence Of Solvent

The influence of solvent effects and hydrogen bond formation on the anharmonicity of the NH stretching vibration of simple secondary amides, lactams, anilides, indole, pyrrole, and imidazole have been studied; and the frequencies of the first and second overtones, their half widths and solvent shifts measured. The validity of Buckingham's theory is established in the case of inert solvents; whereas the second order perturbation treatments are shown to be inapplicable to the case of hydrogen bonding solvents. All NH stretching modes seem to exhibit the same anharmonic behavior which is very different from that of OH vibrations.

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.

DOUBLE AND TRIPLE RESONANCE EXPERIMENTS ON 2-BROMO-5-CHLOROTOLUENE: SIGNS OF THE RING AND RING-METHYL PROTON COUPLING CONSTANTS

1966 ◽  
Vol 44 (22) ◽  
pp. 2743-2747 ◽  
Author(s):  
G. Kotowycz ◽  
T. Schaefer
Keyword(s):  
Coupling Constants ◽  
Para Position ◽  
Triple Resonance ◽  
Triple Resonance Experiments ◽  
Methyl Proton ◽  
Methyl Group ◽  
Meta Position ◽  
Proton Coupling ◽  
Polarization Mechanism ◽  
Exchange Polarization

Tickling and decoupling (triple resonance) techniques show that the ortho, meta, and para proton coupling constants have the same sign in 2-bromo-5-chlorotoluene. If the ortho coupling in the ring is positive, then decoupling experiments show that the methyl proton couplings to the ring protons in the ortho and para position to the methyl group are negative, while that to the meta position is positive. These signs are in agreement with the σ–π exchange polarization mechanism.

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