Atomization dimeric oxides

For amines having an a-hydrogen atom, electrochemical oxidation leads to the imine as the first detectable intemrediate. In the absence of another nucleophile, this is not usually a useful reaction since the imine is hydrolysed by water present in the solvent leading to a mixture of products [80, 81], Oxidation of ten-butylamine, which has no a-hydrogen atom, leads to loss of a proton flrom the nitrogen atom and the dimerization of nitrogen centred radicals. The product isolated in moderate yields is azo-teri-butane 17 [82], The reaction can be carried out in an... 

For the sake of brevity, I have restricted my attention here to M-M bonds of integral order and have considered only the cases where all the available dn electrons are used to form M-M bonds. There are, however, dinuclear compounds having M-M bonds of fractional order (14) and dinuclear compounds in which not all the available dn electrons contribute to M-M bonding. Well known examples of the latter are Cp2Mo2(C0) (MsM) 0 5) and Cp2Mo2(C0)g (M-M) ( 6) compounds which both contain molybdenum atoms in oxidation state number +1 (formally they are d -d dimers), but by considerations of the EAN rule and the observed M-M distances (2.448(1) and 3.235(1) 8) are commonly considered to have M-M triple and single bonds, respectively. 

A final comment is required about the problem of the description of isolated TM atoms on oxide surfaces in general. TM atoms have complex spin states which are not properly described within the DFT approach. Spin-polarized calculations provide a way to take into account the spin properties of the system but some details of the interaction may be described incorrectly. In this respect, the use of wave function-based methods is particularly important for benchmarks and comparisons. This problem is less severe when one considers small clusters where several electronic states exist separated by small energies. But one should be well aware of the fact that the treatment of isolated atoms, dimers, and very small aggregates with DFT methods requires spin-polarized approaches and special care in evaluating the results [199,200]. 

S A. This is consistent with the decreased donor ability of the single-atom bridge with each successive protonation, which promotes longer bond lengths as well as stabilizing the lower dimer oxidation states. 

A detailed understanding of the electronic structure of metal atom dimers and clusters and also small metal oxide clusters is necessary to anticipate... 

The experimentally determined equilibrium constants were combined with the previously evaluated data for the corresponding monoxides to obtain the atomization energies of the dimers. In case of those dimers for which experimental data were missing, the atomization energies were estimated on the assumption that the ratio of atomization of dimeric oxide to its monomeric oxide is constant and equal... 

Oxidative dimerization of various 2-benzyloxy-2-thiazoline-5-ones (222) catalyzed by iodine and triethylamine is another example of the nucleophilic reactivity of the C-4 atom (469) (Scheme 112). Treatment of 212 with pyrrolidinocyclohexene yields the amide (223) (Scheme 113). The mechanism given for the formation of 223 is proposed by analogy with the reactivitx of oxazolones with enamines (4701. 4-Substituted 2-phenylthiazol-5(4Hi-ones react with A -morphoiino-l-cyclohexene in a similar manner (562j. Recently. Barret and Walker have studied the Michael addition products... 

Reactions with Parting of Radicals. The one-electron oxidation of cationic dyes yields a corresponding radical dication. The stabihty of the radicals depends on the molecular stmcture and concentration of the radical particles. They are susceptible to radical—radical dimerization at unsubstituted, even-membered methine carbon atoms (77) (Fig. 6). 

Any substance capable of reacting with free radicals to form products that do not reinitiate the oxidation reaction could be considered to function as free-radical traps. The quinones are known to scavenge alkyl free radicals. Many polynuclear hydrocarbons show activity as inhibitors of oxidation and are thought to function by trapping free radicals [25]. Addition of R to quinone or to a polynuclear compound on either the oxygen or nitrogen atoms produces adduct radicals that can undergo subsequent dimerization, disproportionation, or reaction with a second R to form stable products. 

The Lewis structures of the oxides of nitrogen are shown in Figure 21.6. Two of these species, NO and NO are paramagnetic, with one impaired electron. When nitrogen dioxide is cooled, it dimerizes the unpaired electrons combine to form a single bond between the two nitrogen atoms ... 

In a very recent study, it has been demonstrated116 that zinc 5,15-bis(3,5-di-tert-butylphenyl)-porphyrin (13) without any activating halogen atoms at the chromophore can be directly linked in a very simple oxidative coupling reaction with silver(I) hexafluorophosphate to a mixture of porphyrin dimers, trimers and tetramers. The separation of the product mixture was achieved by gel-permeation chromatography based on the molecular weights of the oligomers. The dimer when re-exposed to the same reaction conditions yielded 25% of the tetramer.116... 

In /r-bridged dimers, two phthalocyanine moieties are linked by one or more bridging atoms such as oxygen or halogens. Niobium(V) oxide tribromide (NbOBr,) when treated with phthalonitrile in 1-chloronaphthalene at 230CC for 3 hours produces /r-bromo-/t-dioxobis[nio-bium(V) phthalocyanine] tribromide in 52%.232... 

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