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.

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.

The effect of solvent on the barrier to internal rotation in p-substituted nitrosoanilines

1975 ◽  
Vol 28 (10) ◽  
pp. 2303 ◽  
Author(s):  
AR Furness ◽  
PD Buckley ◽  
KW Jolley
Keyword(s):  
Internal Rotation ◽  
Line Shape ◽  
Activation Parameters ◽  
Effect Of Solvent ◽  
Solvent Dependence

The solvent dependence of the barrier to internal rotation about the Ar-NO bond in N,N-dimethyl-p-nitrosoaniline and N,N-diethyl-p- nitrosoaniline has been investigated by a complete N.M.R. line-shape method. Activation parameters are reported for the nitrosoanilines in solution in acetone[D6], chloroform[D], and toluene[D8]. The effect of solvent has been found to be small.

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.

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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