Dimerization, mechanisms for

The dimerization mechanism for either the Co or the Fe catalyst system is depicted in Scheme 9 according to the postulation by Hata (65) and Miyake et al. (66). The reaction sequences involve 1,4-addition of the... 

Scheme 9 Proposed dimeric mechanism for ROP of L-lactide initiated by 54 [79]...

Figure 120 Dimerization mechanism for indoles under acidic conditions.

Application of the RRDE as a diagnostic tool to explore the mechanism of an unknown reaction pathway relies, as most methods do, on the differences between the different working curves. For the RDE the working curves for different mechanisms in many cases do not deviate sufficiently to allow a distinction between two possible pathways [259]. The presence of the ring electrode provides extra information, and thus the RRDE is a more sensitive instrument for mechanism analysis. An example is the distinction between the RR and the RS dimerization mechanisms for CS2 radical anion [269]. It has been pointed out, however, that even with this electrode setup the working curves do... 

If association species such as ground-state complexes were suggested to be involved in the dimerization mechanism for coumarin, the rate and the product yield would require that association be much more favored in the solid coumarin than in the inclusion complex, which may be more favorable for the aggregation than the isotropic solution. 

When styrene is refluxed with aqueous sulfuric acid two styrene dimers are formed as the major products One of these styrene dimers is 1 3 diphenyl 1 butene the other is 1 methyl 3 phenyhndan Suggest a reasonable mechanism for the formation of each of these compounds... 

Although the catalysis of the dimerization of aldehydes to acyloins by thiazolium ion has been known for some tlrae, the development of procedures using anhydrous solvents which give satisfactory yields of acyloins on a preparative scale was first realized in the submitters laboratories. The mechanism proposed by Breslow - for the thiazolium ion-catalyzed reactions is similar to the Lapworth mechanism for the benzoin condensation with a thiazolium ylide replacing the cyanide ion. Similar mechanisms are involved... 

The mechanism for the formation of ( )-169 is explained in terms of an intermolecular nucleophilic dimerization. Nucleophilic addition of C-3 of 19 to the 3 position of the initially generated cation 168 gives an imine-nitrone... 

The attack on the aromatic nucleus by hydroxyl radicals is probably analogous to that by phenyl and methyl radicals, Eq. (34a,b). Evidence that the first step is the addition of hydroxyl radical to benzene, rather than abstraction of a hydrogen atom, has recently been adduced from a study of the radiolysis of water-benzene mixtures. The familiar addition complex may undergo two reactions to form the phenolic and dimeric products respectively, Eq. (34a,b). Alternative mechanisms for the formation of the dimer have been formulated, but in view of the lack of experimental evidence for any of the mechanisms further discussion of this problem is not justified. 

A mechanism for its formation was also proposed. Essentially, this involved protonation of 2-methylfuran followed by dimerization and trimerization to a 2,4-difuryl tetrahydrofuran derivative which suffered an acid catalysed cleavage of the saturated ring to produce a carbenium ion possessing an alcoholic function at the other end of... 

Macromonomers such as 66, 68 and 94 are themselves catalytic chain transfer agents (Section 6.2.3.4) and transfer to macromonomer is one mechanism for chain extension of the initially formed species. The adduct species in the case of monomeric radical adding dimer (100) may also react by chain transfer to give 101 which is inert under polymerization conditions (Scheme 6.25). Polymerizations to... 

However in 72% H2SO4 no 86 was observed, but rather dimers 87, 88 and 89 were formed. The mechanism for the dimerization reaction is... 

Ketones are oxidatively cleaved by Cr(VI) or Mn(VII) reagents. The reaction is sometimes of utility in the synthesis of difunctional molecules by ring cleavage. The mechanism for both reagents is believed to involve an enol intermediate.206 A study involving both kinetic data and quantitative product studies has permitted a fairly complete description of the Cr(VI) oxidation of benzyl phenyl ketone.207 The products include both oxidative-cleavage products and benzil, 7, which results from oxidation a to the carbonyl. In addition, the dimeric product 8, which is suggestive of radical intermediates, is formed under some conditions. 

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