Mechanical a process

On the basis of this reaction mechanism, a process for the oxidation of the benzylic position has been developed. This reaction is quite general and proceeds with an excess of 1 at higher temperatures. Over-oxidation of compounds 21 with R = H to the corresponding carboxylic acids was not observed, and the yields of ketones or aldehydes 22 even with labile substrates were generally quite high [21]. 

Adiabatic process (quantum mechanics) — In quantum mechanics a process is called adiabatic if electrons equilibrate with nuclei as they move. The concept of quantum adiabaticity was introduced by Paul Ehrenfest (1880-1933) as early as 1917, using pre-Heisenberg quantum mechanics [i]. The idea survived the advent of post-Heisenberg quantum mechanics, and was brought into its modern form by -> Born [ii]. The existence of adiabatic processes is readily proved by considering... 

The kinetics of the C step are not always first order or pseudo-first order. A second-order reaction will produce qualitatively similar effects to those described above. However, the relative magnitude of the reverse peak current associated with the E step and hence the extent of reversibility and the shift in peak potential will depend on the concentration of the electroactive species for an EC2 mechanism. A process of this type will have a reversible E step at low concentrations or fast scan rates and an irreversible E step at high concentrations or slow scan rates. An example of an EQ-type reaction (Bond et al., 1983, 1989) is the electrochemical oxidation of cobalt (III) tris(dithiocarbamates) (Co(S2CNR2)3) at platinum electrodes in dichloromethane/0.1 M (C4H9)4NPp6 [equations (44) and (45)]. 

Hauser noted that diallyl ether (8) also undergoes Wittig rearrangement upon base treatment and suggested that product formation could involve either a 1,2-shift or a cyclic mechanism (equation 3). Later studies by Schdllkopf and Makisumi with substituted allylic ethers (10,11 and 14-16 equations 4 and 5) pointed to a cyclic (SnO mechanism a process allowed by the Woodward-Hoffmann rules. The diastereoselectivity of the reaction was not determined in these cases, but Schollkopf subsequently found that benzyl rrans-crotyl ether (20 equation 6) affords mainly the anti products upon rearrangement of ether (20) with BuLi in THF. Rautenstrauch observed a 1 1 mixture of syn and anti products upon rearrangement of ether (20) in the presence of TMEDA, whereas the cis isomer (23) gave only the syn product (22 equation 7). ... 

Figure 5.18 displays the temperature dependence of the relaxation rates, as derived from the maxima of the loss curves. For a comparison it also includes the temperature dependencies of the loss maxima of the mechanical a-process, as observed in measurements of either J"( ) G u). As we can... 

Fig. 5.30. Mechanical a-process in LDPE ( Lupolen 1800S ). Loss tangent (top) and temperature dependence of the frequency of the loss peak (bottom) [64]...

The mechanical process requires the presence of both a crystalline and an amorphous component. It does not appear in samples above the melting point. Mats of single crystals with essentially no amorphous phase showed no mechanical a process. Figures 7.50 and 7.51 show the mechanisms of the dielectric and mechanical a processes. They are closely related but not identical. 

Figure 6.19 displays the temperature dependence of the relaxation rate, as derived from the maxima of the loss curves. For a comparison it also includes the temperature dependencies of the loss maxima of the mechanical a-process, as observed in measurements of either J" co) or G" lo). As we can see, the dielectric relaxation rates are located intermediately between the rates obtained in the mechanical experiments and, importantly, all three temperature dependencies are similar, the rates differing only by constant factors. The assignment of this dielectric relaxation process is therefore obvious It originates from the same group of processes as the mechanical a-process and thus is to be addressed as the dielectric a-process. 

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