Dimerization reactions mechanisms

In an investigation to examine the mechanism of this reaction, the dimer (n= 2)... 

Eight variants of the DD reaction mechanism, described by Eqs. (21-25) have been simulated. The simplest approach is to neglect B2 desorption in Eq. (22) and the reaction between AB species (Eq. (25)). For this case, an IPT is observed at the critical point Tib, = 2/3. Thus this variant of the model has a zero-width reaction window and the trivial critical point is given by the stoichiometry of the reaction. For Tb2 < T1B2 the surface becomes poisoned by a binary compound of (A -I- AB) species and the lattice cannot be completely covered because of the dimer adsorption requirement of a... 

Very recently, Fraser et al. (85a) proved, by isolating and analyzing the intermediate, that a similar reaction mechanism is operative in the transition-metal-catalyzed dimerization of norbornadiene. 

The chemical properties of oxide surfaces have been studied by several methods, including oxygen exchange. This method has been used to investigate the mechanisms of heterogeneous reactions for which oxides are active catalysts [36]. The dimerization step does not necessarily precede desorption and Malinin and Tolmachev [634], in one of the few reviews of decomposition kinetics of solid metal oxides, use this criterion to distinguish two alternative reaction mechanisms, examples being... 

Treatment of methano-dimer 28 with elemental bromine revealed a remarkable reactivity at low temperatures it proceeded quantitatively to the furano-spiro dimer 29, by analogy with the ethano-dimer 12 giving spiro dimer 9 upon oxidation. With increasing temperatures, the reaction mechanism changed, however, now affording a mixture of 5-bromo-y-tocopherol (30) and spiro dimer 9 (Fig. 6.24). Thus, the methano-dimer 28 fragmented into an a-tocopherol part, in the form of o-QM 3 that dimerized into 9, and a /-tocopherol part, which was present as the 5-bromo derivative 30 after the reaction. Thus, the overall reaction can be regarded as oxidative dealkylation. 

Durbeej B, Eriksson LA (2002) Reaction mechanism of thymine dimer formation in DNA induced by UV light. Photochem Photobiol A 152 95-101... 

The electrochemistry of cobalt-salen complexes in the presence of alkyl halides has been studied thoroughly.252,263-266 The reaction mechanism is similar to that for the nickel complexes, with the intermediate formation of an alkylcobalt(III) complex. Co -salen reacts with 1,8-diiodo-octane to afford an alkyl-bridged bis[Co" (salen)] complex.267 Electrosynthetic applications of the cobalt-salen catalyst are homo- and heterocoupling reactions with mixtures of alkylchlorides and bromides,268 conversion of benzal chloride to stilbene with the intermediate formation of l,2-dichloro-l,2-diphenylethane,269 reductive coupling of bromoalkanes with an activated alkenes,270 or carboxylation of benzylic and allylic chlorides by C02.271,272 Efficient electroreduc-tive dimerization of benzyl bromide to bibenzyl is catalyzed by the dicobalt complex (15).273 The proposed mechanism involves an intermediate bis[alkylcobalt(III)] complex. 

In this reaction, the enol form of acetone reacts with the Pt(III) dimer complex, and therefore the reaction mechanism seems to be the same with those of the olefin reactions 90). 

Figure 8.2 Reaction mechanism for ethanol oxidation on an Mo dimer/Si02 catalyst as an example of the reaction mode (a) in Figure 8.1...

Another reaction mechanism explaining the observed enhancement of A 0bs values with increasing [amine]o values in S vAr reactions is the dimer mechanism 276, which involves the self-association of the amines277-279 and which (in some cases) may be considered overlapped with mechanism of Scheme 14. A reaction pathway for dimer mechanism is shown in Scheme 17. Considering the zwitterionic intermediate 114 it is possible to have a catalysis in removing the proton and the leaving group (reaction pathway indicated by fc3). 

The 42-residue peptide KO-42 folds in solution into a hairpin helix-loop-helix motif that dimerizes to form a four-helix bundle. On the surface of the folded motif there are six histidines with assigned piC values in the range 5.2 to 7.2 (Fig. 1) and the second-order rate constant for the hydrolysis of mono-p-nitro-phenyl fumarate is 1140 times larger than that of the 4-methylimidazole-cataly-zed reaction at pH 4.1 and 290 K [13]. The reaction mechanism was found to be pH dependent as the kinetic solvent isotope effect was 2.0 at pH 4.7 and 1.0 at pH 6.1 and the pH dependence showed that the reaction rate depended on residues in their unprotonated form with piCj, values around 5. It was thus established that there are functional cooperative reactive sites that contain protonated and unprotonated His residues. 

In this article, the features and mechanism of the crystal-to-crystal reactions of 1,3-diene compounds are described on the basis of the molecular packing structure and intermolecular interactions in the crystals for starting materials and products. The dimerization and isomerization of unsaturated compounds as well as addition polymerization via a chain reaction mechanism are ideal sohd-state reactions, because they produce no leaving group during the reac-... 

Another type of adducts [8, Eq. (3)] was formed by the reaction of di(fert-butyl)aluminum chloride with dilithium bis(trimethylsilyl)hydrazide in low yields below 30% [19]. The structure of 8 consists of a distorted heterocubane with four vertices occupied by nitrogen atoms, two of which are connected by an intact N—N bond across one face of the cube. The cation positions are occupied by two aluminum and two lithium atoms, of which the last ones bridge the N—bond. Part of the hydrazide molecules was cleaved, and the aluminum atoms are bonded to one ferf-butyl group only. On the basis of the NMR spectroscopic characterization many unknown by-products were formed in the course of that reaction, and no information is available concerning the reaction mechanism. Compound 8 may be described as an adduct of dilithium bis(trimethylsilyl)hydrazide to a dimeric iminoalane containing a four-membered AI2N2 heterocycle. Further... 

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