H–D exchange, configurational isomerization, and hydrogenolysis of 1,2-dimethylsilacycloalkanes on copper

1982 ◽  
Vol 0 (19) ◽  
pp. 1089-1090 ◽  
Author(s):  
Mihály Bartók ◽  
Árpád Molnár
Keyword(s):  
Configurational Isomerization

scholarly journals Thermal solid-state Z/E isomerization of 2-alkylidene-4-oxothiazolidines: Effects of non-covalent interactions

2011 ◽  
Vol 76 (3) ◽  
pp. 317-328 ◽  
Author(s):  
Zdravko Dzambaski ◽  
Milovan Stojanovic ◽  
Marija Baranac-Stojanovic ◽  
Dragica Minic ◽  
Rade Markovic
Keyword(s):  
Solid State ◽  
1H Nmr Spectroscopy ◽  
Amorphous State ◽  
Intramolecular Hydrogen Bonding ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Configurational Isomerization ◽  
Non Covalent Interactions ◽  
Intramolecular Hydrogen ◽  
Covalent Interactions

Configurational isomerization of stereo-defined 5-substituted and unsubstituted 2-alkylidene-4-oxothiazolidines 1 in the solid state, giving the Z/E mixtures in various ratios, was investigated by 1H-NMR spectroscopy, X-ray powder crystallography and differential scanning calorimetry (DSC). The Z/E composition can be rationalized in terms of non-covalent interactions, involving intermolecular and intramolecular hydrogen bonding and directional non-bonded 1,5-type S...O interactions. X-Ray powder crystallography, using selected crystalline (Z)-4- oxothiazolidine substrates, revealed transformation to the amorphous state during the irreversible Z ? E process. A correlation between previous results on the Z/E isomerization in solution and now in the solid state was established.

Configurational isomerization in sedimentary bicyclic alkanes

1987 ◽  
Vol 11 (3) ◽  
pp. 151-156 ◽  
Author(s):  
Rohinton A. Noble ◽  
Robert Alexander ◽  
Robert Ian Kagi
Keyword(s):  
Configurational Isomerization

The importance of conformation in the reactivity of radical cations. Changing configuration at saturated carbon centres

1992 ◽  
Vol 70 (1) ◽  
pp. 272-279 ◽  
Author(s):  
Allyson L. Perrott ◽  
Donald R. Arnold
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Molecular Mechanics ◽  
Radical Cation ◽  
Trans Isomer ◽  
Radical Cations ◽  
Singlet Excited State ◽  
Photostationary State ◽  
Configurational Isomerization ◽  
Cis Isomer

Irradiation of an acetonitrile solution of cis 1-methyl-2-phenylcyclopentane (1bcis); 1,4-dicyanobenzene (2), an electron-accepting photosensitizer; and 2,4,6-collidine (3), a nonnucleophilic base, leads to configurational isomerization of the cyclopentane; the photostationary state lies > 99% in favour of the trans isomer. The mechanism proposed for this reaction involves formation of the radical cation of 1bcis by photoinduced electron transfer to the singlet excited state of 2, deprotonation of the radical cation assisted by the base 3, reduction of the resulting benzylic radical by the radical anion [Formula: see text], and reprotonation of the benzylic anion to give both the cis and the trans isomers of 1b. The photostationary state is controlled by the relative rates of deprotonation of the radical cations of 1bcis and trans; these rates are dependent upon the extent of overlap of the SOMO of the radical cation, which is largely associated with the phenyl ring, and the benzylic carbon–hydrogen bond. Molecular mechanics calculations (MM3 and MMP2) are used to calculate the preferred conformations of the isomers. The required orbital overlap is 31% effective with the global minimum conformation of the cis isomer and essentially ineffective for the low-lying conformations of the trans isomer. This proposed mechanism is supported by Stem–Volmer quenching studies, which indicate that both isomers quench the singlet excited state of 2 at the diffusion-controlled rate, and by deuterium incorporation studies. When irradiation of the cis isomer is carried out in acetonitrile–methanol-O-d as solvent, isomerization is accompanied by deuterium exchange at the benzylic position; the trans isomer is stable under these conditions. Keywords: photosensitized electron transfer, radical cation, deprotonation, configurational isomerization, conformation, molecular mechanics (MM3).

The kinetics of specific organic reactions in the zone of catagenesis

1985 ◽  
Vol 315 (1531) ◽  
pp. 107-122 ◽  
Keyword(s):  
Biological Marker ◽  
Rate Coefficients ◽  
Rate Laws ◽  
Oil Generation ◽  
Different Temperatures ◽  
History Of ◽  
Exponential Factors ◽  
Marker Compounds ◽  
Configurational Isomerization ◽  
Kinetics Of

Recently it has been shown that the measured extent of reactions in sedimentary biological marker compounds during catagenesis (for example, steroid aromatization, sterane isomerization) can assist in providing information about the extent of maturation of sedimentary organic matter before and during oil generation and also the thermal history of sediments. In the present study, aromatization of a C 27 C-ring aromatic steroid and isomerization at the chiral centres of an isoprenoid alkane, 6( R ),10( S )-pristane, have been brought about under laboratory conditions, elemental sulphur being used as the source of radicals. Precise rate laws have been determined and rate coefficients measured at different temperatures. The pre-exponential factors and activation energies were found to be 6.7 x 10 12 s -1 and 145 kJ mol -1 for the aromatization, and 2.1 x 10 7 s -1 and 120 kJ mol -1 for the configurational isomerization of pristane. These values reflect the relative behaviour of the two types of reactions in sediments, the aromatization being the more temperature-dependent reaction.

Organic reactions as indicators of the burial and temperature histories of sedimentary sequences

Clay Minerals ◽  
1984 ◽  
Vol 19 (3) ◽  
pp. 271-286 ◽  
Author(s):  
A. S. Mackenzie
Keyword(s):  
Time History ◽  
Reaction Rates ◽  
Organic Reactions ◽  
Temperature History ◽  
Geochemical Data ◽  
Spectrometric Analysis ◽  
Sedimentary Sequences ◽  
Time Histories ◽  
Configurational Isomerization ◽  
Temperature Time

AbstractThree organic reactions which affect individual compounds present in most organic-rich sedimentary rocks have been identified—configurational isomerization and aromatization of steroid hydrocarbons, and configurational isomerization of hopanes. The extents to which these reactions have occurred can be assessed by gas chromatographic-mass spectrometric analysis of the organic extracts of the sediment samples; they provide sensitive indicators of thermal maturation. When combined with the model of sedimentary basin formation by extension of the lithosphere, this molecular approach to the maturation of organic material can be used to constrain the temperature-time histories of sedimentary sequences. This temperature history may be used to integrate the relevant Arrhenius’ and rate equations governing the reaction rates. Each rate equation has three constants—the activation energy, frequency factor and the ratio of forward reaction to backward reaction. These have been estimated using analyses of samples whose temperature-time history is well constrained. The resulting estimates can then be used to reconstruct the temperature-time histories of other samples from organic geochemical data, e.g. calculation of the amount and timing of uplift.

Hydrogenolysis and configurational isomerization of stereoisomeric 1-methyl-3-ethylcyclobutanes on Pt, Pd, and Rh catalysts

1975 ◽  
Vol 24 (9) ◽  
pp. 1904-1909
Author(s):  
O. V. Bragin ◽  
E. G. Khelkovskaya-Sergeeva ◽  
A. V. Preobrazhenskii ◽  
A. L. Liberman
Keyword(s):  
Configurational Isomerization
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