Isomerization temperature effect

The rats of solvolysis of four isomeric tricyclooctane derivatives have been determined. After correction for leaving-group and temperature effects, the relative reactivities are as shown. 

The rate also varies with butadiene concentration. However, the order of the rate dependence on butadiene concentration is temperature-de-pendent, i.e., a fractional order (0.34) at 30°C and first-order at 50°C (Tables II and III). Cramer s (4, 7) explanation for this temperature effect on the kinetics is that, at 50°C, the insertion reaction to form 4 from 3, although still slow, is no longer rate-determining. Rather, the rate-determining step is the conversion of the hexyl species in 4 into 1,4-hexadiene or the release of hexadiene from the catalyst complex. This interaction involves a hydride transfer from the hexyl ligand to a coordinated butadiene. This transfer should be fast, as indicated by some earlier studies of Rh-catalyzed olefin isomerization reactions (8). The slow release of the hexadiene is therefore attributed to the low concentration of butadiene. Thus, Scheme 2 can be expanded to include complex 6, as shown in Scheme 3. The rate of release of hexadiene depends on the concentra-... 

Saltiel, J. and D Agostino, J. (1972) Separation of viscosity aand temperature effects on the singlet pathway to stilbene isomerization, J. Am. Chem. Soc. 94 6445-6456. 

Diynes require somewhat more vigorous conditions for isomerization than 1,4-diynes. Thus, 1,5-hexadiyne is stable to sodium ethoxide in ethanol or 0 03m potassium /-butoxide in /-butyl alcohol at room temperature, but isomerization is effected at higher temperatures or by the use of a higher concentration of potassium /-butoxide- . The reaction is complex, but many of the intricacies have been unravelled, and the relationships are depicted in Scheme... 

Comparative study of the sulfur loss in the xerogel and aerogel sulfated zirconia calcined at different temperatures effect on n-hexane isomerization... 

The cis-trans conversion of mono-unsaturated fatty acids is an equilibrium reaction. Oleic and elaidic acids can be transformed into each other the equilibrium mixture consists of 67 % elaidic acid and 33 % oleic acid, the equilibrium ratio being practically independent on the isomerization temperature (10). This, of course, limits the hardening effect of fatty-oil isomerization processes to a certain extent. 

The presence of an activation barrier for c - t isomerization is definitely demonstrated by the temperature effect on the cis - trans isomerization of 6a, 7a, and 8a from the transient spectroscopy immediately after the laser... 

A combination of different homo- and heteronuclear 2D NMR techniques at 500 MHz have enabled complete assignment of the H and signals of the two conformers of RA-VII in CDCI3 (major conformer conformer A minor one conformer B) [94]. The structures of the two conformers (A and B) in CDCI3 were elucidated based on temperature effects on NH protons, deuterium exchange rate, vicinal coupling constants and NOE experiments (Fig. 27). These conformational analyses showed that the structure of these conformers is a result of geometrical isomerization and that the predominant conformer A exhibits a typical type II P-turn between Ala and Tyr, similar to the crystal structure as analyzed by X-ray diffraction. The minor conformer B exhibits a type VI... 

Temperature Effects, the Reversible Switch between Two-Phase and One-Phase Catalysis. Even the simplest biphasic catalytic system (such as in the case of an isomerization process) contains at least five components two solvents, a reactant, a product, and the catalyst. It is no surprise that the mutual solubilities in such a reaction mixture may vary in a complex way on changing the temperature. Certain biphasic or multiphase liquid mixtures show a sharp... 

Based on these considerations, in order to minimize conformational effects, RPC and HIC separations can be employed at low temperatures, particularly with less robust proteins, i.e., multimeric or multidomain proteins, and polypeptides without significant levels of secondary structure or disulfide connectivities. However, the downside of low-temperature operation may be zone broadening or multiple zones due to the presence of slowly interconverting species such as those associated with cis/trans proline isomerization. Such effects are evident in... 

The first overtone of a free hydroxyl group in dilute CCI4 solution or a low-density gas is at about 7090 cm (1410 nm). This peak is at different positions for primary, secondary, and tertiary alcohols, as seen in Figure 5.1. Primary and secondary butanols can be split into doublets by rotational isomerization. The splits are better seen in Figure 5.2, in the second derivation spectra of the same spectral region. Maeda et al. observed an additional peak in the first overtone region when they subtracted the spectrum at a lower temperature from that at a higher one. They felt that temperature effects further separated species that were weakly bonded to the carbon tetrachloride solvent and a terminal free OH of a self-associated species. 

Estimates of the relative energy difference between the two isomers, A , can be obtained from the relative intensities of the ATD peaks at a temperature where the isomerization has effectively stopped. The equilibrium constant at this energy is given by( >... 

S Saim, B Subramaniam. Isomerization of 1-hexene on Pt/y-Al203 catalyst at subcritical and supercritical reaction conditions pressure and temperature effects on catalyst activity. J Supercrit Fluids 3 214-221, 1990. 

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