Interproton allylic spin-spin coupling involving exocyclic groups

1972 ◽  
Vol 25 (8) ◽  
pp. 1669 ◽  
Author(s):  
GP Newsoroff ◽  
S Sternhell
Keyword(s):  
Coupling Constants ◽  
Spin Coupling ◽  
Dihedral Angles ◽  
Ring Size ◽  
Methylene Groups ◽  
Exocyclic Methylene ◽  
Geminal Coupling ◽  
The Absolute ◽  
Absolute Magnitudes ◽  
Spin Spin Coupling

N.m.r. parameters for 55 compounds incorporating exocyclic groups were obtained. In unstrained structures the relative (as well as the absolute) magnitudes of transoid and cisoid allylic coupling constants depend on the magnitudes of the dihedral angles but additional effects were also identified. The magnitudes of geminal coupling constants between the protons of exocyclic methylene groups and of homoallylic coupling constants involving exocyclic ethylidene and isopropylidene groups vary systematically with ring size.

Molecular orbital and 1H nuclear magnetic resonance studies of the inversion potentials of thianthrene and thioxanthene

1991 ◽  
Vol 69 (6) ◽  
pp. 927-933 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Christian Beaulieu
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Basis Set ◽  
Basis Sets ◽  
Inversion Barrier ◽  
H Nmr ◽  
Methylene Groups ◽  
Spin Spin Coupling ◽  
Split Valence

The inversion potentials, obtained from STO-3G, STO-3G(*), 3-21G, 3-21G(*), and 4-31G basis sets, are reported for thianthrene and thioxanthene, molecules in which both or only one of the methylene groups have been replaced by sulfur in 9,10-dihydroanthracene. Comparison with the available experimental data suggests that the split-valence bases lead to an overestimate, possibly by about 10 kJ/mol, of the inversion barrier in the crystal, whereas the STO-3G and STO-3G* basis sets underestimate this barrier. It appears that the inversion barrier for thianthrene is much lower in solution than in the crystal. The long-range coupling constants between the methylene and ring protons for thioxanthene in solution are consistent with an inversion barrier somewhat smaller than those obtained with the split-valence bases but rather larger than those predicted with the STO-3G basis set. The bond lengths and angles in the equilibrium structures of the two molecules, as computed with the 3-21G(*) basis, agree reasonably well with those in their crystals, except that the theoretical folding angles are smaller than measured. These discrepancies become less marked when expectation values are calculated from the theoretical inversion potentials at finite temperatures. Key words: MO calculations, inversion potentials of thianthrene and thioxanthene; 1H NMR, thioxanthene; spin–spin coupling constants, long range, in thioxanthene.

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.

The Proton–Proton and Proton–Carbon-13 Spin–Spin Coupling Constants in 1,3-Dioxole and Bis-1,3-dioxolyl. Conformational Dependence

1975 ◽  
Vol 53 (18) ◽  
pp. 2734-2741 ◽  
Author(s):  
Ted Schaefer ◽  
Kalvin Chum ◽  
David McKinnon ◽  
M. S. Chauhan
Keyword(s):  
Double Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Dihedral Angles ◽  
Proton Proton ◽  
Proton Coupling ◽  
Vicinal Proton ◽  
Karplus Relationship ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The carbon-13 satellite peaks in the proton magnetic resonance spectra of 1,3-dioxole and bis-1,3-dioxolyl are analyzed under single and double resonance conditions to yield the signs and magnitudes of proton–proton coupling constants over three, four, and five bonds, and of proton–carbon-13 coupling constants over one, two, and three bonds. The conformational behavior of bis-1,3-dioxolyl contrasts sharply with that of analogous sym-tetrasubstituted ethane derivatives. It is indicated that the two-bond proton–carbon-13 coupling in the ethanic fragment can be used for conformational analysis in a manner similar to vicinal proton–proton couplings. The vicinal three-bond proton–carbon-13 couplings are given for dihedral angles of 180 and 120° and their relative magnitudes are as expected from a Karplus relationship. The two-bond proton–carbon-13 coupling in the olefinic fragment is, at 20.0 Hz, the largest coupling known for such a bond.

Influencing of Ring Size on Germinal Interproton Coupling Constants in Exocyclic Methylene Groups

1985 ◽  
Vol 38 (6) ◽  
pp. 889 ◽  
Author(s):  
RJ Spear ◽  
S Sternhell
Keyword(s):  
Experimental Data ◽  
Substituent Effects ◽  
Size Reduction ◽  
Coupling Constants ◽  
Ring Size ◽  
Methylene Groups ◽  
Exocyclic Methylene

In systems where substituent effects are constant, there is a well defined trend in the magnitude of geminal interproton coupling constants in exocyclic methylene groups with ring size. Reduction of ring size from six to five to four results in a monotonic reduction in the magnitude of Jgem. These trends apply to methylenecycloalkanes , methylenebenzocycloalkenes and α- methylenecycloalkanones . There is an indication that the trend does not continue for methylenecyclopropanes. A number of new exocyclic-methylene compounds have been designed and synthesized to provide specific experimental data.

The use of three-bond spin-spin coupling constants in the determination of conformations of molecules in solution

1975 ◽  
Vol 345 (1640) ◽  
pp. 61-72 ◽  
Keyword(s):  
Conformational Changes ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Dihedral Angles ◽  
Ion Binding ◽  
Coupling Constant ◽  
Conformational Studies ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Over the last 15 years, the use of three-bond 1 H - 1 H spin coupling constants (3 -/HH) for obtaining stereochemical and conformational information has become a well-established procedure. The method relies on the relation (originally pointed out by Karplus) between 3J HH and cos 2 < Ø) where Ø is the dihedral angle in the H -X -Y -H fragment. This method is particularly successful when applied to a series of related molecules for which the form of 3J HHØ relation has been determined experimentally. The method can be used (1) for defining dihedral angles in molecules of fixed conformation; (2) for determining the fractional populations of conformers in a mixture of rapidly interconverting conformers and thus to check potential energy calculations; (3) in conjunction with studies of lanthanide induced shifts (l.i.s.) since any acceptable conformational solution must agree with both the coupling constant and l.i.s. data; (4) to monitor any conformational changes which might take place on lanthanide ion binding. Three-bond coupling constants involving other nuclei such as 13 C, 14 N and 31 P can also be used for conformational analysis. The various applications of three-bond coupling constants to conformational studies of peptides and choline analogues will be considered.

Vibrational and thermal averaging of the indirect nuclear spin-spin coupling constants of CH4, SiH4, GeH4 and SnH4

1997 ◽  
Vol 91 (5) ◽  
pp. 897-907 ◽  
Author(s):  
SHEELA KIRPEKAR ◽  
THOMAS ENEVOLDSEN ◽  
JENS ODDERSHEDE ◽  
WILLIAM RAYNES
Keyword(s):  
Nuclear Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling
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