Long-range hydrogen-fluorine spin-spin coupling. Further support for the "through-space" (direct) mechanism

1971 ◽  
Vol 93 (24) ◽  
pp. 6532-6536 ◽  
Author(s):  
E. Abushanab
Keyword(s):  
Long Range ◽  
Spin Coupling ◽  
Direct Mechanism ◽  
Spin Spin Coupling

Long-range proton-fluorine spin-spin coupling. Further evidence for a 'direct' mechanism

1973 ◽  
Vol 26 (12) ◽  
pp. 2659 ◽  
Author(s):  
W Adcock ◽  
SQA Rizvi
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Variable Temperature ◽  
Strong Support ◽  
Spin Coupling ◽  
Coupling Mechanism ◽  
Direct Mechanism ◽  
Spin Spin Coupling

A variable temperature p.m.r. study of outho- and peri-acetyl substituted fluoro-naphthalenes (including o-fluoroacetophenone) has been carried out. Further, 1-fluoro- 8-methylnaphthalene (previously unknown) has been synthesized and its p.m.r. spectra has been measured at various temperatures. The data, together with 19F substituent chemical shifts (SCS) for ortho-substituted cyanofluoronaphthalenes, provide further strong support for a through-space coupling mechanism (JMe,F).

Long-range proton-fluorine spin-spin coupling and 19F substituent chemical shifts (SCS) in the naphthalene ring system

1971 ◽  
Vol 24 (9) ◽  
pp. 1829 ◽  
Author(s):  
W Adcock ◽  
DG Matthews ◽  
SQA Rizvi
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Naphthalene Ring ◽  
Methyl Proton ◽  
Direct Mechanism ◽  
Spin Coupling Constants ◽  
Proton Resonances ◽  
Spin Spin Coupling

A number of acetyl-substituted fluoronaphthalenes have been synthesized and their fluorine as well as proton N.M.R. spectra have been measured. The methyl proton resonances of these derivatives appeared as a doublet which indicated long-range coupling with the fluorine. It was observed that the coupling (JMe,F) for 3-acetyl-2-fluoronaphthalene and o- fluoroacetophenone is independent of the magnitude of the 19F substituent chemical shifts (scs) which are shown to be sensitive indices of the bond-order differences in naphthalene (C 1 and C 2; C 2 and C 3) and benzene. Furthermore, the magnitude of the long-range proton-fluorine spin-spin coupling constants are solvent dependent. The data are clearly in accord with a predominant contribution of a ?direct? mechanism to the proton-fluorine spin-spin coupling.

scholarly journals Signs of proton–proton and proton–fluorine spin–spin coupling constants in 2-fluoro-3-methylpyridine. Sigma and pi contributions to coupling in a nitrogen heterocycle

1969 ◽  
Vol 47 (9) ◽  
pp. 1507-1514 ◽  
Author(s):  
T. Schaefer ◽  
S. S. Danyluk ◽  
C. L. Bell
Keyword(s):  
Nitrogen Atom ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nitrogen Heterocycle ◽  
Triple Resonance ◽  
Triple Resonance Experiments ◽  
Proton Proton ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The signs of all proton–proton and proton–fluorine spin–spin coupling constants in 2-fluoro-3-methylpyridine have been determined by double and triple resonance experiments. The signs of the longrange coupling constants, JH,CH3 and JF,CH3 are the same as in fluorotoluene derivatives. Their magnitudes are consistent with the assumption that the nitrogen atom primarily polarizes the σ bonds in the molecule, leaving the π contribution to the long-range coupling relatively unaffected.

Molecular Conformation of 4-Thiouridine in Aqueous Solution

1971 ◽  
Vol 49 (14) ◽  
pp. 2449-2452 ◽  
Author(s):  
F. E. Hruska ◽  
K. K. Ogilvie ◽  
A. A. Smith ◽  
H. Wayborn
Keyword(s):  
Aqueous Solution ◽  
Long Range ◽  
Crystalline State ◽  
Molecular Conformation ◽  
Spin Coupling ◽  
Pyrimidine Nucleoside ◽  
Coupling Interaction ◽  
X Ray ◽  
Anti Conformation ◽  
Spin Spin Coupling

β-4-Thiouridine is a component of several tRNA molecules. A recent X-ray study has shown that this pyrimidine nucleoside favors the syn conformation in the crystalline state. The 100 and 220 MHz p.m.r. data and a comparison with those of uridine are presented here. A long-range five-bond spin–spin coupling interaction between the H-5 and -1′ hydrogens is noted. The results are consistent with an anti conformation for 4-thiouridine in an aqueous solution.

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.

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