Atom migration mechanism

Photochemistry. Vinyl chloride is subject to photodissociation. Photexcitation at 193 nm results in the elimination of HCl molecules and Cl atoms in an approximately 1.1 1 ratio (69). Both vinyUdene ( B2) [2143-69-3] and acetylene have been observed as photolysis products (70), as have H2 molecules (71) and H atoms [12385-13-6] (72). HCl and vinyUdene appear to be formed via a concerted 1,1 elimination from excited vinyl chloride (70). An adiabatic recoil mechanism seems likely for Cl atom elimination (73). As expected from the relative stabiUties of the 1- and 2-chlorovinyl radicals [50663-45-1 and 57095-76-8], H atoms are preferentially produced by detachment from the P carbon (72). Finally, a migration mechanism appears to play a significant role in H2 elimination (71). 

The rearrangement (automerization) of Dewar thiophene 5-oxide (61), observed by NMR, occurs so much more rapidly than that of the corresponding episulfide that special mechanisms have been invoked. The one which involves a zwitterionic intermediate (Scheme 108) is favored over a pseudopericyclic sulfur-walk mechanism in which the electrons of the carbon-sulfur o--bond and the pair of electrons on sulfur exchange places as the sulfur atom migrates around the ring (80JA2861). 

We have also observed competition between products resulting from C-C and C-H bond activation in reactions of Y with propene,138 propyne,143 2-butyric,143 four butene isomers,138 acetaldehyde,128 acetone,128 ketene,144 and two cyclohexadiene isomers,145 as well as for Zr, Nb, Mo, and Mo with 2-butyne.143 In this chapter, we use the term C-C activation to describe any reaction leading to C-C bond fission in which the hydrocarbon reactant is broken into two smaller hydrocarbon products, with one hydrocarbon bound to the metal. It is important to note, however, that C-C activation does not necessarily require true C-C insertion. As will be shown in this chapter, the reaction of Y, the simplest second-row transition metal atom, with propene leads to formation of YCH2 +C2H4. The mechanism involves addition to the C=C bond followed by H atom migration and C-C bond fission, rather than by true C-C insertion. 

These results combined with the total suppression of copolymerization in the presence of hydroquinone as inhibitor indicate that hydrostannylation takes place upon the polyaddition of diorganostannane to the epoxyolefine by a radical mechanism accompanied by hydrogen atom migration in each chain propagation, No addition of organostannanes to the oxirane ring was observed 98>. 

The Favorskii rearrangement is an example of a migration to an electron rich carbon atom. Its mechanism with... 

Two mathematical models for sintering mechanisms for supported metals have been put forward (1) a particle migration model where particles migrate over the surface of the support, collide and fuse, causing loss in dispersion (e.g. Ruckenstein et al 1984) and (2) an atomic migration model involving the... 

The initial reaction of C11 with olefins is perhaps an addition to the double bond followed by electronic rearrangement, rupture of a C—C bond, and hydrogen atom migration in the resulting hot intermediate to give the observed products. Further experimental work may provide conclusive evidence for such a mechanism. 

The inversion of configuration at the iron atom in Eq. (13) is in accord with the proposed alkyl migration mechanism for the decarbonylation reaction22,32,12K... 

Figure 3.10 Examples of a CO insertion and b CH3 migration, in a square-planar Pd complex with a P—N chelating ligand. Note that the migration mechanism retains the cis configuration between the CO group and the chelate nitrogen atom.

A more rigorous approach to calculating the diffusion coefficients has been adopted by Kikuchi [165], A binary substitution alloy (s = 3) has been considered with the vacancy mechanism of atom migration. He was the first to take account of the temporal correlations and to obtain expressions for the correlation cofactor fc in the non-ideal systems. The derived coefficients satisfy Onsager s reciprocal relations. 

Stereochemical Aspects The configuration of the product of the /Mysine 2,3-aminomutase reaction was established to be 3S,5S by NMR spectroscopic comparison of the d-lactam of the 3,5-diaminohexanoic acid 45 from C. sticklandii with authentic samples of both pairs of diastereomers [71]. The stereochemical mechanism of the / -lysine 5,6-aminomutase reaction was investigated by means of tritium labeling. It turned out that the pro-5 S hydrogen atom migrates to position 6 in the 3,5-diaminohexanoic acid [72] (Scheme 1.6.16). 

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