Hydrolysis of phosphoranes containing a perfluoropinacolyl ring

1983 ◽  
Vol 61 (10) ◽  
pp. 2264-2267 ◽  
Author(s):  
Alexander F. Janzen ◽  
Alberta E. Lemire ◽  
Ronald Kirk Marat ◽  
Alan Queen
Keyword(s):  
Shape Analysis ◽  
Variable Temperature ◽  
Exchange Process ◽  
Activation Parameters ◽  
Ir Studies ◽  
Line Shape Analysis ◽  
Acidic Conditions ◽  
Hydrolysis Of ◽  
Trifluoromethyl Groups ◽  
C Nmr

The hydrolysis of phosphoranes Ph2P(pfp)Cl, Ph2P(pfp)OR, PhP(pfp)(OR)2, and (RO)3P(pfp), containing a perfluoropinacolyl (pfp) ring, occurs under neutral, basic, or acidic conditions and leads to the formation of acyclic perfluoropinacolyl products, i.e. R2P(O)OC(CF3)2C(CF3)2OH, as determined by 1H, 19F, 31P, 13C nmr and ir studies. In the presence of a base, all trifluoromethyl groups in Ph2P(O)OC(CF3)2C(CF3)2OH are equilibrated, as verified by 19F and 13C nmr; and from the variable temperature 19F nmr line-shape analysis the activation parameters for this exchange process were found to be: Ea = 36.0 ± 3 kJ mol−1, ΔH≠ = 33.5 ± 3 kJ mol−1, ΔS≠ = −86 ± 8 J K−1 mol−1, [Formula: see text]. The reactions of phosphoranes with HF were briefly investigated.

Effects of substitution on nitrogen on barriers to rotation of cyclic amides. Part I. Investigation of the rotational barier in 4-benzoyl-1-thia-4-azacyclohex-2-ene by 1H dynamic nuclear magnetic resonance spectroscopy

1977 ◽  
Vol 55 (6) ◽  
pp. 949-957 ◽  
Author(s):  
T. Bruce Grindley ◽  
B. Mario Pinto ◽  
Walter A. Szarek
Keyword(s):  
Variable Temperature ◽  
Activation Parameters ◽  
Resonance Spectroscopy ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Line Shape Analysis ◽  
Chemical Shift Data ◽  
Dynamic Nuclear Magnetic Resonance ◽  
Shift Data ◽  
C Nmr

The rotational barrier in 4-benzoyl-1-thia-4-azacyclohex-2-ene has been investigated by total line-shape analysis of variable temperature 1H nmr spectra in acetonitrile-d3. Separate treatment of the vinyl and methylene signals yielded sets of values for activation parameters which were in excellent agreement. Assignment of the major and minor rotational isomers was made from chemical-shift data derived from the 13C nmr spectrum at 243 K in acetonitrile-d3.

The Barrier to Rotation About the N—N Bond in N-Nitrosamines as Determined by Nuclear Magnetic Resonance Total Line Shape Analysis

1974 ◽  
Vol 52 (17) ◽  
pp. 3028-3036 ◽  
Author(s):  
J. D. Cooney ◽  
S. K. Brownstein ◽  
J. W. ApSimon
Keyword(s):  
Shape Analysis ◽  
Line Shape ◽  
Energy Barrier ◽  
Activation Parameters ◽  
Substantial Contribution ◽  
Resonance Structure ◽  
Bond Rotation ◽  
Line Shape Analysis ◽  
Bond Character ◽  
Nitrogen Bond

The energy barrier to internal N—N bond rotation in five cyclic and two bicyclic N-nitrosamines [Formula: see text]has been determined using high temperature 100 MHz n.m.r. spectroscopy. A substantial contribution from the ionic resonance structure of [Formula: see text] produces considerable double bond character in the nitrogen–nitrogen bond and a concomitant increase in the rotational barrier about the N—N bond. The molecules were examined in the[Formula: see text]liquid state and had ring sizes varying from five to nine atoms. The Arrhenius and Eyring activation parameters for the energy barrier were determined using total line shape analysis and the intensity ratio approximation method. The energy barrier to N—N bond rotation was found to range from 23–29 kcal/mol depending on the molecular structure and the solvent.

Nuclear Magnetic Resonance Studies of Enantiomeric Internal Rotational Isomers of 1- and 3-Arylhydantoins in Achiral and Chiral Solvents

1975 ◽  
Vol 53 (11) ◽  
pp. 1556-1562 ◽  
Author(s):  
Lawrence D. Colebrook ◽  
Siddik Icli ◽  
Frank H. Hund
Keyword(s):  
Internal Rotation ◽  
Shape Analysis ◽  
Chemical Shifts ◽  
Activation Parameters ◽  
Methyl Groups ◽  
Solvent Interactions ◽  
Rotational Isomers ◽  
Line Shape Analysis ◽  
Solvent Dependence ◽  
Normal Probe

1H and 13C n.m.r. spectra have been determined for a number of 1- and 3-arylhydantoins in achiral and chiral solvents. These compounds, which have enantiomeric rotational isomers, show restricted internal rotation about the aryl C—N bond at normal probe temperatures. Chemical shifts between corresponding protons on the pairs of rotamers, induced by diastereomeric solute–solvent interactions in the chiral solvent, are strongly dependent on the location of the protons in the solute molecules. In conjunction with 1H and 13C chemical shifts, these data provide information on the geometry of the solvated species. No splitting of signals resulting from the presence of diastereomeric solvates was observable in the 13C spectra. Activation parameters for hindered internal rotation, determined by complete p.m.r. line shape analysis using signals of the diastereotopic methyl groups in the 5-position, show some solvent dependence.

Applications of Proton Magnetic Resonance to Rotational Isomerism in Halotoluene Derivatives. V. α,α,α′,α′,2,3,5,6-Octachloro-p-xylene, Semiempirical Barrier Calculations

1971 ◽  
Vol 49 (5) ◽  
pp. 789-795 ◽  
Author(s):  
B. H. Barber ◽  
T. Schaefer
Keyword(s):  
Shape Analysis ◽  
Proton Magnetic Resonance ◽  
Activation Parameters ◽  
Rotational Isomerism ◽  
Standard Errors ◽  
Energy Functions ◽  
Potential Energy Functions ◽  
Rate Dependent ◽  
Line Shape Analysis ◽  
Cis And Trans

In toluene-d8 solution the p.m.r. spectrum of α,α,α′,α′,2,3,5,6-octachloro-p-xylene at temperatures below −25 °C consists of two sharp peaks corresponding to the two conformations in which the methine protons lie cis and trans to each other in the plane of the aromatic ring. The barrier to rotation of the dichloromethyl groups is derived from a line-shape analysis of the rate-dependent spectra using the computer program ABXFIT. The activation parameters are EA = 13.6 ± 0.4 kcal/mol, log A = 11.3 ± 0.3, ΔH‡ = 13.1 ± 0.4 kcal/mol, ΔS‡ = −7.3 ± 1.3 e.u., ΔG‡ = 15.4 kcal/mol at 286 °K. The quoted errors are standard errors from least squares fits. These parameters are compared to the extensive data known for α,α,2,4,6-pentachlorotoluene. A series of barrier calculations, based on modified Buckingham and on van der Waals potential energy functions, are discussed with reference to various halotoluenes.

NMR Investigations of the Pitch Dependence of Self-diffusion in Cholesteric Liquid Crystals

1988 ◽  
Vol 43 (7) ◽  
pp. 687-692 ◽  
Author(s):  
S. Oehler ◽  
R. Stannarius ◽  
H. Schmiedel
Keyword(s):  
Activation Energy ◽  
Liquid Crystals ◽  
Shape Analysis ◽  
Line Shape ◽  
Nmr Spectra ◽  
Self Diffusion ◽  
Line Shape Analysis ◽  
Twisted Nematic ◽  
Nematic Phases ◽  
C Nmr

Abstract Self-diffusion in the isotropic and twisted nematic phases of mesogenic substances has been studied by means of 1H- and 13C-NMR.From the line shape analysis of the recorded 13C-NMR spectra we obtained the diffussion coefficient D⊥ along the helical pitch.Various concentrations of a chiral additive changed the pitch P0 of a nematic mixture of phenyl-benzoates from 4.7 μm to 7.8 μm. The measured values of D⊥ were in the range from 2.4 · 10-12 m2 s-1 to 1.9 · 10-11 m2 s-1 We found an Arrhenius behaviour with an activation energy of about 55 kJ/mole nearly independent of the pitch. The obtained data for D⊥ seem to have a lower than quadratic dependence on P0.

Lanthanide complexes of an oxazoline-phenoxide hybrid chelate

2005 ◽  
Vol 83 (5) ◽  
pp. 449-459 ◽  
Author(s):  
David J Berg ◽  
Chuanjian Zhou ◽  
Tosha Barclay ◽  
Xuening Fei ◽  
Shengyu Feng ◽  
...  
Keyword(s):  
Shape Analysis ◽  
Line Shape ◽  
Variable Temperature ◽  
Paramagnetic Nmr ◽  
Dynamic Features ◽  
X Ray ◽  
X Ray Crystallography ◽  
Line Shape Analysis ◽  
Mechanistic Investigation ◽  
Bailar Twist

The synthesis of 2-(2′-hydroxy-3′-allylphenyl)-4,4-dimethyl-2-oxazoline, H-Allox (3), and lanthanide tris chelate complexes, mer-Ln(Allox)3 (Ln = La (4), Ce (5), Sm (6), Er (7), and Y (8)), derived from it are reported. A six-coordinate mer geometry without alkene coordination was confirmed in the solid state by X-ray crystallography for 5 and 7. Variable-temperature NMR experiments suggested that this is the most stable isomer in solution as well, although the inequivalent ligand environments undergo rapid averaging at room temperature for all five complexes. A mechanistic investigation indicated that this fluxional process is an intramolecular six-coordinate rearrangement, but it was not possible to distinguish between a Bailar (trigonal) or Rây–Dutt (rhombic) twist. Kinetic parameters for the fluxional process were determined by line shape analysis for 8 yielding ΔH‡ = 24 ± 2 kJ mol–1 and ΔS‡ = –99 ± 10 J mol–1 K–1. The structural and dynamic features of 4–8 were compared with the related In, Ga, and Al tris(2-oxazolylphenoxides).Key words: oxazoline, phenoxide, lanthanide, Group 3, Rây–Dutt twist, Bailar twist, Eyring plot, X-ray crystallography, mer isomer, variable-temperature NMR, line shape analysis, dynamic NMR, paramagnetic NMR, bidentate ligands.

Phenylfluorophosphoranes: axial–equatorial fluorine exchange in RC6H4PF3H and intermolecular exchange in the PhPF2(H)OMe–MeOH–base system

1990 ◽  
Vol 68 (3) ◽  
pp. 488-491 ◽  
Author(s):  
Leonard J. Kruczynski ◽  
Alberta E. Lemire ◽  
Kirk Marat ◽  
Alexander F. Janzen
Keyword(s):  
Shape Analysis ◽  
Ligand Exchange ◽  
Activation Parameters ◽  
Base System ◽  
Dynamic Nmr ◽  
Nmr Spectrum ◽  
First Order ◽  
H Nmr ◽  
Line Shape Analysis ◽  
Nmr Study

Activation parameters for axial–equatorial fluorine exchange in arylfluorophosphoranes RC6H4PF3H, where R = o-CF3, m-CF3, p-CF3, m-CH3, were studied by the dynamic nmr technique: [Formula: see text] varied between 53 and 56 kJ mol−1.The synthesis of difluoromethoxyphenylphosphorane, PhPF2(H)OMe, from PhPF2 and MeOH is catalyzed by small amounts of Et3N, pyridine, PhPF3H, or HF. Rapid intermolecular ligand exchange occurs in PhPF2(H)OMe after addition of methanol and a base such as triethylamine or pyridine. Under these conditions, exchange of fluorine, hydrogen, and methoxy ligands occurs, as shown by 1H, 19F, and 31P nmr. From a line shape analysis of the 31P{1H} nmr spectrum, the rate of P—F cleavage was found to be first order (1.17 ± 0.2) in Et3N concentration, with [Formula: see text] = 50 kJ mol−1 and ΔS# = −67 J mol−1 deg−1.An equilibrium constant of 1.8 at 25 °C was found for the reaction of PhPF2(H)OMe with PhPF2.Keywords: axial–equatorial fluorine exchange in RC6H4PF3H intermolecular exchange in the PhPF2(H)OMe–MeOH–base system; 31P and 19F nmr study of ligand exchange in phosphoranes.

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