Shift s. a. Migration, Position

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

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... 

It is of interest that the reversible migration of hydrogen between positions 1 and 2 of thi.s sj stem corre.spond to a 1,5-sigmatropie shift, a proee.s.s predicted to be favorable on theoretical grounds [R. R. Woodward and R. Hoffmann, J. Am. Ghem. Soc. 87, 2511 (1965)] and known to occur with exceptional facility (R. B. Woodward in Aromaticity, Spec. Publ. No. 21, p. 217. The Chemical Society, London, 1967). 

Carboxylic esters are produced by the addition of carboxylic acids to olefins, a reaction that is usually acid-catalyzed (by proton or Lewis acids182) and similar in mechanism to 5-4. Since Markovnikov s rule is followed, hard-to-get esters of tertiary alcohols can be prepared from olefins of the form R2C=CHR.183 When a carboxylic acid that contains a double bond in the chain is treated with a strong acid, the addition occurs internally and the product is a y- and/or a 8-lactone, regardless of the original position of the double bond in the chain, since strong acids catalyze double bond shifts (2-2).184 The double bond always migrates to a position favorable for the reaction, whether this has to be toward or away from the carboxyl group. Carboxylic esters have also been prepared by the acyloxymercuration-demercuration of olefins (similar to the procedures mentioned in 5-2 and 5-4).185... 

In mammalian liver microsomes, cytochrome P-450 is not specific and catalyzes a wide variety of oxidative transformations, such as (i) aliphatic C—H hydroxylation occurring at the most nucleophilic C—H bonds (tertiary > secondary > primary) (ii) aromatic hydroxylation at the most nucleophilic positions with a characteristic intramolecular migration and retention of substituents of the aromatic ring, called an NIH shift,74 which indicates the intermediate formation of arene oxides (iii) epoxidation of alkenes and (iv) dealkylation (O, N, S) or oxidation (N, S) of heteroatoms. In mammalian liver these processes are of considerable importance in the elimination of xenobiotics and the metabolism of drugs, and also in the transformation of innocuous molecules into toxic or carcinogenic substances.75 77... 

The CO of Ihe acetyl ligand has a choice of four cis positions into which it may shift, displacing the CO that is already there. One of these sites is occupied by CO. Thus we would predict that 25% of the product would have no CO and the other 75% would have a CO ligand cis to the methyl group. Experimentally it is found that 25% of the product is devoid of tagged CO. 25% of the product has CO Irans to CH. and 50% of the product has CO cis to CH,. Therefore CO insertion must be eliminated as a mechanistic possibility, a methyl migration mechanism, however. i.s consistent with these experimental results. 

When the isoxazole (105.1) is treated with an excess of diazomethane at laboratory temperature, a [1, S]sigmatropic shift occurs and the benzoyl group migrates from the bridgehead position to an adjacent carbon (that derived from diazomethane)—a move which resembles the Van Alphen-Hauttel rearrangement [B-4]. 

---