N.M.R. spectra of 'p-nitrosophenol' and its methyl derivatives

1966 ◽  
Vol 19 (5) ◽  
pp. 841 ◽  
Author(s):  
RK Norris ◽  
S Sternhell
Keyword(s):  
Aqueous Solutions ◽  
Long Range ◽  
Organic Solvents ◽  
Negative Charge ◽  
Spin Coupling ◽  
Potassium Salts ◽  
Methyl Derivatives ◽  
Spin Spin Coupling

On the basis of N.M.R. spectra, supported by u.v. and i.r. data, it can be concluded that "p-nitrosophenol" and several of its methyl derivatives exist predominantly in the benzoquinone monoxime form in organic solvents and that in aqueous solutions the corresponding potassium salts have the negative charge largely on the oxime oxygen. The protons on the α-carbon syn to the quinone monoxime hydroxyl are deshielded with respect to the anti protons but this relationship appears to be reversed in the anions. The N.M.R. spectra of some p-nitrosoanisoles and quinone monoxime methyl ethers are given and syn-anti equilibria and long-range spin-spin coupling are discussed.

Sigma and Pi Electron Contributions to Long-range Spin–Spin Coupling Constants in the Methyl Derivatives of the Fluoropyridines

1972 ◽  
Vol 50 (14) ◽  
pp. 2344-2350 ◽  
Author(s):  
J. B. Rowbotham ◽  
T. Schaefer
Keyword(s):  
Nitrogen Atom ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Mechanism ◽  
Methyl Group ◽  
Spin Coupling Constants ◽  
Methyl Derivatives ◽  
Spin Spin Coupling ◽  
Derivatives Of

Seven methyl derivatives of the 3- and 4-fluoropyridines are synthesized and their p.m.r. spectra are analyzed. The nuclear spin–spin coupling constants are compared with previous results for the four methyl derivatives of 2-fluoropyridine. A model in which the nitrogen atom polarizes primarily the σ electron system of the ring, leaving the π electron contribution to the coupling mechanism relatively unaffected, qualitatively accounts for the large majority of the coupling constants. For example, the coupling over six bonds between methyl protons and a fluorine nucleus, [Formula: see text] is the same whether the fluorine atom or the methyl group is placed ortho to the nitrogen atom and is little different from its value in p-fluorotoluene. The model is consistent with significant σ electron contributions to long-range couplings over four and five bonds from methyl protons to fluorine nuclei or ring protons. Evidence is adduced for resonance structures in which fluorine conjugates with nitrogen or with ring carbon atoms. An earlier suggestion, that hyperconjugation of the methyl group with nitrogen is necessary to the interpretation of the observed couplings, is dropped. Instead, a substantial polarization of the σ electron core near C-2 and -6 is invoked but apparently does not extend appreciably beyond these atoms in the ring.

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.

A proton magnetie resonance and molecular orbital study of the conformational preferences of the vinylic fragment in some 2-vinylfurans and in 2-vinylthiophene

1976 ◽  
Vol 54 (20) ◽  
pp. 3216-3223 ◽  
Author(s):  
William J. E. Parr ◽  
Roderick E. Wasylishen ◽  
Ted Schaefer
Keyword(s):  
Molecular Orbital ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Side Chain ◽  
Orbital Theory ◽  
Molecular Orbital Study ◽  
Conformational Preferences ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The stereospecific spin–spin coupling constants over five bonds between the α-proton in the side chain and the protons in the heterocycle in 2-vinylfuran, in its β-nitro and β-aldehydic derivatives, and in 2-vinylthiophene are used to demonstrate the preponderance of the s-trans conformers in polar and nonpolar solutions. These conclusions are compared with predictions made by molecular orbital theory at the STO-3G, INDO, CNDO/2, and MINDO/3 levels. Long-range coupling constants between the protons in the side chain and protons in the heterocycle are calculated by CNDO/2 and INDO–MO–FPT and are compared with experiment. It is concluded that the five-bond couplings involving the α-proton are most sensitive to conformation and that they are transmitted mainly via a σ electron mechanism. The other long-range coupling constants are discussed in terms of σ and π electron mechanisms. The STO-3G calculations yield barriers to internal rotation of greater than 4.8 kcal/mol.

Sign in / Sign up

Export Citation Format

Share Document