Shift s. a. Migration

Polysacdiarides s. Disacdiarides Polysolfides s. Trisulfides Position shift (s. a. Migration, Rearrangement)... 

Semicorrins, synthesis 26, 796 Sensitizers (s. a. Triplet sensitizers) acetone 26,720 acetophenone 26, 763 N,N-dimethylaniline 26, 85 fluorenone 22, 761 suppl. 26 methylene blue 26, 125 xylene 26, 135, 146 Sequestering agent s. Sodium pyrophosphate Shift b. a. Migration,... 

RB3LYP calculations indicate that the s-cis conformer of peroxy acids is more stable than the s-trans conformer. Calculations on the reaction of prop-2-enol with some peroxy acids showed that trans-transition states collapse to the epoxide via a 1,2-shift, whereas a 1,4-shift is operable for cis-transition states.195 Quantum mechanical calculations have been performed on the migration step of the Baeyer-Villiger rearrangements of some substituted acetophenones with m-chloroperbenzoic acid (m-CPBA). The energy barriers, charge distributions and frontier molecular orbitals, determined for the aryl migration step, have been used to explain the effects of substituents on the reactivity of the ketones.196... 

Presumably this reaction proceeds via an allylic carbocation intermediate 301 formed by Lewis acid-initiated C-S cleavage, then ring closure to a new carbocation 302 stabilized by the silyl group. As illustrated in Scheme 55, the subsequent steps, leading to final product 300, involve disulfide bond formation, double-bond shift, and hydride migration. 

However we rationalized that using silicon as a migrating group could result in a unique stabilization of the energy surface of olefin isomerization. This rationalization was based on silicon s well known ability to stabilize both a-carbanions and p-carbocations. Thus a hypothetical "dual-stabilized" zwitterion would be produced by a 90° twist of a vinyl silane, and a following 1,2-shift of Silicon would produce a singlet carbene possessed of the same hyperconjugative stabilization as in a P-silyl cation (Eq. 5). 

Komatsu et al. have developed unique methods for the generation of 1,3-dipoles from organosilanes (Scheme 10.222). Linder thermal conditions, N-(a-silylbenzyl) imines and -amides are converted, via 1,2- or 1,4-silatropic shift of the silyl group, into azomefhine ylides (153 from the amide) which react with dipolarophiles [578]. Similar thermal 1,4-silyl migrations of a-silylnitrosamines and S-a-silylben-zyl thioesters provide convenient routes to azomethine imines 154 [579] and fhio-carbonyl ylides 155 [580], respectively. 

In the RCFE effluent 1s continuously reinjected into the chamber via recycle streams as indicated in Figure 2. Each recycle stream reinjection port is offset from its corresponding elution port by a specified lateral distance, S, so that upon recycle the effluent is shifted back against the solute s electrophoretic migration. When the shift is small solute migrates in the positive z direction but if the shift is increased sufficiently... 

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