Control rearrangement

The mass balance considerations and calculations illustrate how concentrations of these elements are controlled. Rearranging equation 16, we have... 

Ring expansion by rearrangement Controlling rearrangements Using rearrangements in synthesis Insertion of O, N, or C next to a ketone... 

The stereochemical course of 1,2 rearrangements is comparable to chelation-controlled rearrangements (see p 3420), and the chairlike transition state predominates. Despite the fixed vinyl double-bond geometry, however, the stereochemical outcome from these reactions indicates more or less intermediacy of the boatlike geometry, as observed in ortho ester rearrangements520- 52 h... 

Better results are obtained in chelation-controlled rearrangements of (E)- or (Z)-derivatives 3592. These rearrangements proceed with known internal asymmetric induction [e.g., anti for the ( -substrate because of the change in the chain see Section 1.6.3.1.1.4.], and with respect to the relative asymmetric induction the syn relationship is preferred. 

Figure 26 Illustration of the chemistry of a Switch-ester segment as a reversible structure breaking unit that forms kinks in the peptide backbone (left) and the pH-value-controlled rearrangement in the switch unit, resulting in the native peptide backbone by an O N acyl transfer rearrangement (middle and right). Analogs of the fully synthetic aramidic polymers (bottom) Nomex as a well-processable polymer with kinks in the main chain (left) and Kevlar as a polymer, which is difficult to handle due to strong chain-chain interactions (right).

Fig. 5.2.8 Proposed transition state for ligand controlled rearrangement.

A gold-catalyzed intramolecular alkenylsilylation reaction was reported and this unusual conversion was recently studied by DFT calculations. The electrophilic gold (I) catalyst is thought to generate carbocation and silyl cation intermediates in the conversion. The computational results suggest that the bistrifiimide anion modulates the reactivities of the cationic intermediates and controls rearrangement steps in the reaction. 

Equation 18-32 can be used to interpret further the relative gain array of a 2 X 2 process. Assuming that y2 is kept at its set point of zero under closed-loop control, rearranging (18-32) gives... 

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