Electric moments and conformation of substituted fluoroformates in benzene solutions

1968 ◽  
Vol 46 (10) ◽  
pp. 1645-1648 ◽  
Author(s):  
E. Bock ◽  
D. Iwacha ◽  
H. Hutton ◽  
A. Queen
Keyword(s):  
Dipole Moment ◽  
Long Range ◽  
Fluorine Atom ◽  
Dipole Moments ◽  
Experimental Results ◽  
Spin Coupling ◽  
Coupling Mechanism ◽  
Methyl Ethyl ◽  
Hydrocarbon Group ◽  
Spin Spin Coupling

The dipole moments of methyl-, ethyl-, n-propyl-, n-butyl-, n-amyl-, and phenyl-fluoroformate were determined in dilute benzene solutions at 25 °C. The experimental results suggest that the conformation of the fiuoro-esters is similar to the conformation of the chloro-esters and differs from the conformation of the normal esters; viz. the ester hydrocarbon group and the fluorine atom are cis to each other. Results of fluorine and proton n.m.r. measurements on these molecules support the conclusions based on the dipole moment data if a "through-space" coupling mechanism is assumed for the long range spin–spin coupling JH–F1−5.

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).

The conformational distribution of 2-cyanobenzaldehyde and 3-cyanobenzaldehyde in solution and in the vapor

1991 ◽  
Vol 69 (7) ◽  
pp. 1039-1046 ◽  
Author(s):  
Ted Schaefer ◽  
Kerry J. Cox ◽  
Rudy Sebastian
Keyword(s):  
Long Range ◽  
Dipole Moments ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Orbital Theory ◽  
Spectral Parameters ◽  
Proton Proton ◽  
H Nmr ◽  
Proton Coupling ◽  
Spin Spin Coupling

The 1H nuclear magnetic resonance spectra of 2-cyanobenzaldehyde (2CNB) and 3-cyanobenzaldehyde (3CNB) in CS2/C6D12 and acetone-d6 solutions at 300 K yield precise stereospecific long-range proton–proton coupling constants. These are used to establish the conformational population of the o-cis and o-trans conformers of these relatively polar molecules. For example, the fractional o-cis population of 2CNB changes from 0.12(4) in CS2/C6D12 to 0.46(6) in acetone-d6, whereas that of 3CNB is 0.48(2) in both solvents. Extrapolation to the vapor phase, using a dielectric model, implies a negligible concentration of the o-cis conformer of 2CNB and a roughly 50% abundance of each conformer of 3CNB. Computations at various levels of molecular orbital theory provide estimates of the rotational barrier of the aldehyde moiety and confirm the planar structure of each conformer. The geometries of three conformers are given as obtained from the 6-31G MO basis and may be useful to molecular spectroscopists. Theoretical and experimental dipole moments are interpolated to yield estimates of their magnitudes for the four planar conformers. Somewhat less precise 1H nmr spectral parameters (than for the above solutions) are also obtained for dilute solutions in benzene-d6 at 300 K. The conformational distributions based on these parameters are compared with their only other measurement, based on dipolar moments in benzene at 298 K. Good agreement between the results of the two methods is found for 3CNB but not for 2CNB. It is suggested that specific interactions occur between benzene solvent and solute molecules, particularly for 3CNB, for which these interactions stabilize the conformer having a low dipole moment. Remarkable changes in the intraring proton–proton coupling constants occur in going from CS2/C6D12 to acetone-d6 solution. Key words: 2- and 3-cyanobenzaldehyde (2CNB and 3CNB): 1H NMR, conformations, long-range spin–spin coupling constants, MO computations.

Dipole moments of substituted chloroformates in dilute benzene solutions

1967 ◽  
Vol 45 (24) ◽  
pp. 3177-3179 ◽  
Author(s):  
E. Bock ◽  
D. Iwacha
Keyword(s):  
Chlorine Atom ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Experimental Results ◽  
Methyl Ethyl ◽  
Hydrocarbon Group

The dipole moments of methyl, ethyl, n-propyl, n-butyl, amyl, and phenyl chloroformate as well as n-butyl formate in dilute benzene solution at 25 °C were determined. The experimental results suggest that the configuration of the chloro-esters differs from the configuration of the unchloroinated esters, viz. the ester hydrocarbon group and the chlorine atom are cis to each other.

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.

A solid-state 31P NMR study of 1:1 silver–triphenylphosphine complexes — Interpretation of 1J(107,109Ag,31P) values,

2009 ◽  
Vol 87 (7) ◽  
pp. 1090-1101 ◽  
Author(s):  
Fu Chen ◽  
Se-Woung Oh ◽  
Roderick E. Wasylishen
Keyword(s):  
Solid State ◽  
Spin Coupling ◽  
Coupling Mechanism ◽  
P Values ◽  
X Ray Crystallography ◽  
Phosphine Complexes ◽  
Nmr Study ◽  
Fermi Contact ◽  
Spin Spin Coupling ◽  
Cp Mas Nmr

High-resolution solid-state 31P NMR spectroscopy was used to investigate a series of 1:1 silver–triphenylphosphine complexes, [Ph3PAgX]n, where X is a monovalent anion and n = 1, 2, 3, 4, or ∞. The 31P CP MAS NMR spectra reveal the number of distinct phosphorus sites in these complexes as well as the |1J(109Ag,31P)| values, which range from 401 ± 10 Hz (X = N3–) to 869 ± 10 Hz (X = SO3CF3–). The data obtained here and in earlier investigations indicate that |1J(109Ag,31P)| values for silver–tertiary phosphine complexes decrease as Ag–P bond lengths increase. This experimental conclusion is supported by DFT calculations, which also indicate that the Fermi-contact mechanism is the only important spin–spin coupling mechanism for 1J(109Ag,31P) in these complexes. In addition, the crystal structure of a silver–triphenylphosphine trifluoroacetate tetramer was determined using X-ray crystallography, and the structure of a silver–triphenylphosphine chloride tetramer was reinvestigated.

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.

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