Concerning the extension of the J method for internal barriers to six-bond couplings to 19F in the 4-fluorophenyl fragment

1978 ◽  
Vol 56 (18) ◽  
pp. 2442-2446 ◽  
Author(s):  
Ted Schaefer ◽  
Werner Danchura ◽  
Walter Niemczura ◽  
James Peeling
Keyword(s):  
Ground State ◽  
Proton Magnetic Resonance ◽  
Coupling Constants ◽  
Side Chain ◽  
Fluorine Nucleus ◽  
Proton Proton ◽  
Proton Coupling ◽  
Carbon Carbon Bond ◽  
Internal Barriers

The long-range coupling constants over six bonds from the side-chain protons to the fluorine nucleus on the ring are extracted from the proton magnetic resonance spectra of p-fluorobenzyl cyanide, chloride, and bromide; of p-fluorobenzal chloride; and of p-fluoroisopropylbenzene. On the assumption that these couplings are transmitted via a σ–π mechanism, a hindered rotor treatment yields the barriers to internal rotation about the carbon–carbon bond which attaches the substituent to the benzene ring. These barriers, when compared to those derived from the analogous proton–proton coupling constants, apparently are accurate enough for the determination of ground state conformations and for a rough assessment of the energetics of conformational interconversions.

The internal barriers to rotation about the carbon–carbon bond in 3,5-dichlorobenzyl alcohol and selenol by the J method

1978 ◽  
Vol 56 (13) ◽  
pp. 1721-1723 ◽  
Author(s):  
Ted Schaefer ◽  
Werner Danchura ◽  
Walter Niemczura ◽  
William J. E. Parr
Keyword(s):  
Internal Rotation ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Side Chain ◽  
Carbon Carbon Bond ◽  
Carbon Carbon Bonds ◽  
Spin Coupling Constants ◽  
Internal Barriers ◽  
Spin Spin Coupling

The J method, depending on a comparison between observed spin–spin coupling constants over six bonds between protons on a side chain and para ring protons and those calculated by a hindered rotor treatment, is applied to the determination of the twofold barrier to internal rotation about the carbon–carbon bonds in 3,5-dichlorobenzyl alcohol and selenol. In the alcohol, the C—O bond prefers the benzene plane by 0.3 ± 0.2 kcal/mol whereas, in the selenol, the C—Se bond prefers a plane perpendicular to the benzene ring by 3.8 ± 0.7 kcal/mol. Comparison with the thiol suggests that a major component of the barrier arises from repulsive interactions, increasing as the size of the XH (X = O, S, Se) group increases.

21,22-Disubstituted 18α,19βH-Ursane Derivatives with Oxabicyclooctane System in Ring E

1993 ◽  
Vol 58 (1) ◽  
pp. 173-190 ◽  
Author(s):  
Eva Klinotová ◽  
Jiří Klinot ◽  
Václav Křeček ◽  
Miloš Buděšínský ◽  
Bohumil Máca
Keyword(s):  
Spectral Data ◽  
Spin Systems ◽  
Coupling Constants ◽  
Complete Analysis ◽  
Nmr Spectrum ◽  
Proton Proton ◽  
H Nmr ◽  
Proton Coupling ◽  
C Nmr

Reaction of 3β-acetoxy-21,22-dioxo-18α,19βH-ursan-28,20β-olide (IIIa) and 20β,28-epoxy-21,22-dioxo-19α,19βH-ursan-3β-yl acetate (IIIb) with diazomethane afforded derivatives XII-XIV with spiroepoxide group in position 21 or 22, which were further converted into hydroxy derivatives XV and XVII. Ethylene ketals VIII-X were also prepared. In connection with the determination of position and configuration of the functional groups at C(21) and C(22), the 1H and 13C NMR spectral data of the prepared compounds are discussed. Complete analysis of two four-spin systems in the 1H NMR spectrum of bisethylenedioxy derivative Xb led to the proton-proton coupling constants from which the structure with two 1,4-dioxane rings condensed with ring E, and their conformation, was derived.

Through-space or proximate 19F,19F and 19F,1H spin–spin coupling constants in some benzenesulfonyl fluoride derivatives

1976 ◽  
Vol 54 (22) ◽  
pp. 3564-3568 ◽  
Author(s):  
William J. E. Parr ◽  
Ted Schaefer
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Side Chain ◽  
Conformational Preference ◽  
Fluorine Nucleus ◽  
Spin Coupling Constants ◽  
The Difference ◽  
Spin Spin Coupling

The analysis of the fluorine and proton magnetic resonance spectra of 2,4,6-trimethylbenzenesulfonyl fluoride and of 2,5-difluorobenzenesulfonyl fluoride yields the signs and magnitudes of the spin–spin coupling constants containing a through-space component. The coupling between the fluorine nucleus and the methyl protons over five bonds is +1.9 Hz, opposite in sign to the −3.1 Hz observed for the corresponding coupling in 2,6-dimethylbenzoyl fluoride. The difference of 5 Hz is possibly a consequence of the different conformational preference of the SO2F and COF substituents. The coupling over four bonds between the fluorine nucleus on the side chain and that on the ring is +11.6 Hz in 2,5-difluorobenzenesulfonyl fluoride. It is argued that this value indicates a preference of the S—F bond for a plane lying, on average, nearly perpendicular to the benzene ring. Similar indications are noted for pentafluorobenzenesulfonyl fluoride and for pentafluorobenzenesulfinyl fluoride.

Proton Magnetic Resonance Studies of Rotational Isomerism in Halotoluenes. X. Estimates of Conformational Preferences and Rotational Barriers in Benzal Fluoride and Some Dichloro Derivatives

1974 ◽  
Vol 52 (3) ◽  
pp. 481-488 ◽  
Author(s):  
J. Brian Rowbotham ◽  
Alexander Frank Janzen ◽  
James Peeling ◽  
Ted Schaefer
Keyword(s):  
Magnetic Resonance ◽  
Long Range ◽  
Proton Magnetic Resonance ◽  
Substituent Effects ◽  
Molecular Orbital Calculation ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Proton Proton ◽  
Carbon Carbon Bond ◽  
Dichloro Derivative

The synthesis of benzal fluoride and of its 2,6-, 3,5-, 3,4-, and 2,4-dichloro derivatives is followed by an analysis of their proton magnetic resonance spectra. The long-range spin–spin coupling constants are most consistent with a barrier to rotation about the sp2–sp3 carbon–carbon bond in benzal fluoride of less than 500 cal/mol, in semiquantitative agreement with an ab initio molecular orbital calculation. The 2,6-dichloro derivative has a conformation in which the C—H bond of the side chain lies in the plane of the aromatic ring. The 2,4-dichloro derivative favors a similar conformation, the C—H bond lying cis to the ring chlorine atom. In contrast to the long-range proton–proton couplings, the long-range proton–fluorine couplings are intrinsically sensitive to substituent effects from the ring chlorine atoms.

1H and 19F NMR conformational studies of the monofluorostyrenes in solution. Comparison with theory and vapor phase behavior

1990 ◽  
Vol 68 (8) ◽  
pp. 1383-1392 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Side Chain ◽  
Coupling Constant ◽  
Mo Calculations ◽  
Carbon Carbon Bond ◽  
Electron Contribution ◽  
Internal Barriers ◽  
Cis And Trans ◽  
Coupling Mechanisms

The parameters for the high resolution 1H and 19F NMR spectra of 2-, 3-, and 4-fluorostyrene are reported for solutions in CS2 and acetone-d6 at 300 K. The populations of the planar cis and trans conformers of 2- and 3-fluorostyrene are deduced from the long-range coupling constants involving the meta and α protons. These populations are insensitive to solvent and appear to be in reasonable agreement with previous 6-31G MO computations for the free molecule; they are also compared with populations deduced from recent rotational and vibronic spectra. The long-range coupling constants for the protons of 4-fluorostyrene imply an internal barrier to rotation about the exocyclic carbon–carbon bond very similar to that in styrene, in agreement with the 6-31G results. The signs of the coupling constants involving 19F and the protons in the side chain are reported and discussed in terms of coupling mechanisms for the three molecules. An earlier surmise, of a positive a electron contribution to the coupling constant over six bonds in an all-trans arrangement, is confirmed for the meta and trans-β protons in 3-fluorostyrene. Keywords: monofluorostyrenes, 1H and 19F NMR, conformations, long-range coupling mechanisms, MO calculations of internal barriers.

2 J HH -resolved HSQC: Exclusive determination of geminal proton-proton coupling constants

2017 ◽  
Vol 282 ◽  
pp. 18-26 ◽  
Author(s):  
Núria Marcó ◽  
Pau Nolis ◽  
Roberto R. Gil ◽  
Teodor Parella
Keyword(s):  
Coupling Constants ◽  
Proton Proton ◽  
Proton Coupling ◽  
Geminal Proton

Transoid Homoallylic Proton-Proton Coupling Constants

1989 ◽  
Vol 42 (5) ◽  
pp. 659 ◽  
Author(s):  
M Barfield ◽  
RJ Spear ◽  
S Sternhell
Keyword(s):  
Angular Dependence ◽  
Substituent Effects ◽  
Coupling Constants ◽  
Mo Calculations ◽  
Proton Proton ◽  
Proton Coupling ◽  
Tentative Assignment ◽  
Single Compound ◽  
Derivatives Of

Transoid homoallylic coupling constants (5JH,H) for six compounds (5,10-dihydroindeno[2,1-alindene and confertifolin derivatives) of fixed stereochemistry were determined and compared with calculated values. Magnetic equivalence limited discrete determination of 5Jtrans and 5Jcis to three of these compounds. The single compound where unequivocal assignment could be made revealed 5Jtrans > 5Jcis; this was supported in two other compounds by tentative assignment. Changes in the magnitude of the couplings suggested that substantial substituent effects may be operative. INDO-MO calculations correctly predicted the angular dependence but incorrectly predicted 5Jcis > 5Jtrans.

Proton Magnetic Resonance Studies of Rotational Isomerism in Halotoluenes VIII. Stereospecific 1H–9F Coupling Constants and Conformations of some Fluoro and Chloro Derivatives of Benzalchloride

1971 ◽  
Vol 49 (12) ◽  
pp. 2033-2036 ◽  
Author(s):  
H. M. Hutton ◽  
J. B. Rowbotham ◽  
B. H. Barber ◽  
T. Schaefer
Keyword(s):  
Proton Magnetic Resonance ◽  
Rotational Isomerism ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Side Chain ◽  
Fluorine Nucleus ◽  
Spin Coupling Constants ◽  
Chloro Derivatives ◽  
Spin Spin Coupling ◽  
Derivatives Of

In solution the 2-fluoro-5-chloro-, 2-fluoro-6-chloro-3-nitro-, 2-fluoro-6-chloro-5-nitro-, and 2,4,5-trichloro-benzalchlorides prefer conformations in which the C— bond of the side-chain lies in the plane of the aromatic ring. This C—H bond eclipses that ortho C—X bond (X = H, F, Cl) in which X is smaller than Y = H, F, Cl in the C—Y bond, also ortho to the dichloromethyl group. The long-range spin–spin coupling constants between the proton in the side-chain and the ring protons or fluorine nucleus are stereospecific. In particular, the coupling over four bonds between the side-chain proton and the ring fluorine is −0.3 Hz when the C—H and C—F bonds are arranged cis to each other but is −2.5 Hz when these bonds have a transoid planar arrangement.

Sign in / Sign up

Export Citation Format

Share Document