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.

The effect of substituents on geminal proton–proton coupling constants

1967 ◽  
Vol 45 (21) ◽  
pp. 2481-2487 ◽  
Author(s):  
Robert R. Fraser ◽  
Paul Hanbury ◽  
C. Reyes-Zamora
Keyword(s):  
Resonance Spectrum ◽  
Coupling Constants ◽  
Molecular Orbital Theory ◽  
Coupling Constant ◽  
Orbital Theory ◽  
Proton Proton ◽  
Proton Coupling ◽  
Geminal Proton ◽  
Geminal Coupling ◽  
Methylene Group

A series of 2-benzyloxytetrahydropyrans bearing substituents at the ortho, meta, and para positions of the benzene ring have been synthesized. From the nuclear magnetic resonance spectrum of each compound, the geminal coupling constant (J) between the non-equivalent protons of the benzylic methylene group was determined. The geminal coupling constant for the methylene group of several benzyl sulfoxides was also measured. In the ether series it was found that J varied from 11.1 to 13.3 c.p.s. and was directly proportional to the Hammett σ value for the meta and para substituents. In the sulfoxides, however, J was unaffected by the substituent. On the basis of the molecular orbital theory of geminal coupling constants and steric considerations, it is proposed that the sensitivity of J to the substituent effect is dependent upon the conformation of the molecules with respect to the Ar—CH2 bond. The potential utility of this relation as a method of conformational analysis is discussed.

The Effect of Substituents on Geminal Proton–Proton Coupling Constants; a Conformational Dependence. II

1971 ◽  
Vol 49 (5) ◽  
pp. 755-760 ◽  
Author(s):  
Robert R. Fraser ◽  
Roger N. Renaud
Keyword(s):  
Conformational Analysis ◽  
Solvent Effects ◽  
Coupling Constants ◽  
Methylene Carbon ◽  
Proton Proton ◽  
Proton Coupling ◽  
Geminal Proton ◽  
Methylene Groups ◽  
Geminal Coupling ◽  
Methylene Group

The effect of para-substituents on the geminal coupling constants in benzylic methylene groups has been studied as a function of the conformation at the benzene—CH2 bond. The slopes of Hammett plots of Jgemvs. σ are large (−1.6 to −1.9) when the geometry permits a hyperconjugative interaction between the benzene ring and the methylene group but negligible (+ 0.2) when this interaction is geometrically restricted. The effect of a change in electronegativity of the group attached to the methylene carbon has also been investigated. The change in the slope, ρ, from −1.7 to −1.6 on protonation of the nitrogen attached to the methylene group in a series of isoindolines shows this effect to be extremely small. Solvent effects on ρ are also very small. The potential of this J − σ relation for conformational analysis of benzyl groups is discussed in comparison with existing methods.

PROTON MAGNETIC RESONANCE SPECTRUM OF 1-PHENYLCYCLOPROPYLCARBOXYLIC ACID: A2B2 SPECTRA OF CYCLOPROPANES

1963 ◽  
Vol 41 (10) ◽  
pp. 2429-2438 ◽  
Author(s):  
H. M. Hutton ◽  
T. Schaefer
Keyword(s):  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Carbon Disulphide ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Spectral Parameters ◽  
Saturated Ring ◽  
Geminal Coupling ◽  
Range Of Values ◽  
Qualitative Discussion

A2B2 spectra of 1,1 -disubstituted cyclopropanes have been calculated over a range of values of the spectral parameters. The sign of the geminal coupling is opposite to that of the vicinal couplings. Since this is also the case with other saturated ring systems the theoretical spectra should be useful in studies of other saturated ring systems.The shifts and coupling constants are given for the protons in 1-phenylcyclopropylcarboxylic acid in solution in carbon disulphide, chloroform, and benzene as an example of the A2B2 analysis. The ring protons in 1-phenylcyclopropylcarbinol were found to be equivalent in different solvents, with insignificant coupling to the protons in the methylene and phenyl groups. A qualitative discussion of the shifts of the various protons in various solvents is given.

Das Protonenresonanzspektrum von orientiertem Benzol in nematisch-kristallinflüssiger Lösung

1965 ◽  
Vol 20 (4) ◽  
pp. 572-580 ◽  
Author(s):  
Alfred Saupe
Keyword(s):  
Magnetic Resonance ◽  
Chemical Shift ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Scalar Coupling ◽  
Small Temperature ◽  
Theoretical Methods ◽  
Experimental Errors

The proton magnetic resonance spectrum of benzene oriented in a nematic solution is calculated using group theoretical methods. The calculations agree within experimental errors with the spectrum of benzene observed in a nematic solution of 4.4′-di-n-hexyloxy-azoxy-benzene. By an improvement of the temperature homogenity in the sample it was possible to obtain linewidths of only about 5 cps for all lines independent of the splitting. It is confirmed that the signs of the scalar coupling constants between ortho and meta protonpairs are positive. A small temperature dependence of the chemical shift of the benzene protons was found in the nematic solution. It is due to the dependence of the average orientation on the temperature.

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.

CORRELATION OF ETHYLENIC PROTON COUPLING CONSTANTS WITH THE ELECTRONEGATIVITY OF SUBSTITUENTS INTERPRETATION OF THE DEVIATIONS OF BROMO AND IODO SUBSTITUENTS

1965 ◽  
Vol 43 (10) ◽  
pp. 2827-2833 ◽  
Author(s):  
F. Hruska ◽  
G. Kotowycz ◽  
T. Schaefer
Keyword(s):  
Linear Relationship ◽  
Coupling Constants ◽  
Box Model ◽  
Coupling Constant ◽  
Vinyl Bromide ◽  
Proton Coupling ◽  
Vinyl Iodide ◽  
Cis And Trans

It is shown that for the geminal, cis and trans proton coupling constants in vinyl bromide and vinyl iodide there exist significant deviations from an inverse linear relationship between coupling constants and the electronegativity of the substituent in monosubstituted ethylenes. By an adaptation of the box model of Juan and Gutowsky to the 13C—H coupling constants in the system CH2 = CHX, it is shown that there are related anomalies in the 13C—H coupling constants in vinyl bromide and vinyl iodide. A comparison of the three types of 13C—H coupling constants in some vinyl compounds suggests that there may be an interaction between the substituent and the C—H bond which affects the coupling constant but not the s-character of the carbon orbital in the bond.

Substituent effects on geminal proton–proton coupling constants

1970 ◽  
Vol 48 (13) ◽  
pp. 2134-2138 ◽  
Author(s):  
Y. L. Chow ◽  
S. Black ◽  
J. E. Blier ◽  
M. M. Tracey
Keyword(s):  
Carbon Tetrachloride ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Coupling Constants ◽  
Proton Proton ◽  
Proton Coupling ◽  
Geminal Proton ◽  
Geminal Coupling ◽  
Hammett Σ Constants

The geminal coupling constants between the non-equivalent benzylic protons of a series of para- and meta-substituted N-benzyl-2-methylpiperidines were shown to be proportional to the Hammett σ constants of the substituents with ρ −1.38 in carbon tetrachloride, −1.21 in benzene, and nearly 0 in 1 N DCl solutions. The ρ values were compared with those of other series and were discussed in terms of the possible conformations involved. The chemical shifts of the benzylic protons of the piperidine derivatives did not give a good correlation with the Hammett σ constants in these solvents.

The effect of substituents on geminal proton–proton coupling constants. III

1977 ◽  
Vol 55 (14) ◽  
pp. 2642-2648 ◽  
Author(s):  
Roger N. Renaud ◽  
John W. Bovenkamp ◽  
Robert R. Fraser ◽  
Raj Capoor
Keyword(s):  
Coupling Constants ◽  
Coupling Constant ◽  
Mo Calculations ◽  
Proton Proton ◽  
Effect Of Substituents ◽  
Proton Coupling ◽  
Geminal Proton ◽  
Geminal Coupling ◽  
The Difference ◽  
Methylene Group

The effect of substituents at the 3-position in a series of N-methyl 5,6-dihydro-7H,12H-di-benzo[c,f]azocines on the geminal coupling constants of the C-12 methylene protons has been determined. The slope of the Hammett plot of 2J vs. σ has been found to be +0.20. The orientation of the methylene protons with respect to the π orbitals of the benzene ring bearing the substituent is such that no hyperconjugative effect should be present. The value of +0.20 is in contrast to a previously measured slope of −1.9 for compounds having a geometry ideal for hyperconjugative effects and substantiates the predictions of theoretical MO calculations. As a result, the reliability of this conformational dependence of ρ for use in conformational analysis has been strengthened.A comparison of the data for the azocines with those in the literature indicates the difference between the minimum and maximum effects of a phenyl substituent on a geminal coupling constant of an attached methylene group is 5.5 Hz.

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.

Hétérobicycles oxygénés. Synthèse d'alkyl-3,6,8-trioxabicyclo[3.2.1]octanes et d'alkyl-3,7,9 et -4,7,9-trioxabicyclo[4.2.1]nonanes

1978 ◽  
Vol 56 (17) ◽  
pp. 2292-2300 ◽  
Author(s):  
Pierre Calinaud ◽  
Jacques Gelas
Keyword(s):  
Double Bond ◽  
Carbon Atom ◽  
Nmr Spectra ◽  
Membered Ring ◽  
Coupling Constants ◽  
Basic Medium ◽  
Main Interest ◽  
Proton Coupling ◽  
Geminal Proton

The cyclization in a basic medium of 2 (or 4)-chloroalkyl-4 (or 2) -hydroxyalkyl-1,3-dioxolanes leads to bicyclic acetals, the 3,6,8-trioxabicyclo[3.2.1]octanes, which are useful intermediates for synthesis, yielding notably functionalized 1,4-dioxanes. The nmr spectra of these heterobicyclics were studied. The geminal proton coupling constants permit oneto distinguish between five- and six-membered rings and the determination of couplings over several bonds (4J and 5J) yields information concerning the conformation of the model bicyclics.Two isomeric series of alkylated bicyclic acetals (3,7,9- and 4,7,9-trioxabicyclo[4.2.1]nonanes) are accessible by the following routes: (a) the intramolecular addition of a 4-hydroxy-alkyl group to the ethylenic double bond on the carbon atom a to C-2 in the 1,3-dioxolanes; (b) the dechlorohydration of 2-chloromethyl-4-hydroxyalkyl-1,3-dioxolanes; (c) the dehydration of dioxolane-diols. The main interest in these heterobicyclics is to prepare a seven-membered ring and to be able to prepare functionalized 1,4-dioxepanes. [Journal translation]

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