O dimerization

A number of publications have appeared on the synthesis of cationic cobalt(I) complexes by known routes. The cations are of the well-established type [Co(CNR)5]+ (R = aryl) (119-122). Reactions of aromatic isocyanides with Co2(CO)g in refluxing toluene have given the fully substituted cobalt(O) dimer Co CNR) (R = xylyl, C6H2Me3-2,4,6, C6H2Br-4-Me2-2,6) (25,123). 

Stern-Volmer plot of the quenching of acenaphthylene In els (O) and trans (O) dimer formation by ferrocene. (Reproduced by permission from the Journal of American Chemical Society. 104. 4635,... 

O dimers may appropriately be called peroxy anions, 022 . In a silicate matrix they appear to occur as peroxy links or, more generally, peroxy entities, X/00 Y where X,Y = Si4+,A13+, Fe3+... Chemically a peroxy entity represents an extra oxygen it may be called an interstitial oxygen atom though this does not correctly convey the covalent binding in the 0-0 bond. 

The numerous known flavin dimer species are reviewed in Table II. Apart from the normal very unstable quinhydrone 7r-complex (15, 16), which can only be observed in protic media, and apart from the stable biflavins obtained irreversibly by a Michael-type alkali-catalyzed selfcondensation of flavoquinone (22), there are two further types of o-dimers known besides the above one, namely the 7<, 4a-product of phosphate-catalyzed photodimerization (23) and the 5,5 -deazaflavin dimer (24), which is discussed below. 

The high-field resonances (—563 and —568 ppm) are assigned to H-O dimers of (HPS)VO+ based on the concentration-dependent variation of their signal areas relative to those of (HPS)V0(0H)/(HPS)V02. The monomer (HPS)VO+ is chiral, so dimerization gives rise to d, 1, and meso diastereomers, which contain three vanadium environments. The upfield resonances at —563 and —568 ppm can be fit to three curves (—564, —567, and —568 ppm) in the appropriate ratios ( 2 1 1), consistent with dimerization. 

Figure 4. Time dependence of monomer(o), dimer(e) and trimer(n) of N-700 latex particles at 25°C. [NaCl]=l M.

Oxidative coupling of aUelfydesJ Aliphatic aldehydes bearing an ci-hydrogcn atom on treatment with activated manganese dioxide undergo x-hydrogen abstraction and C-C and C-O dimerization. For example, isobutyraldehyde (I) is converted in about... 

Figure 4-50 The sequential interaction model of allosteric enzymes. As each site is occupied, the subunit carrying the site undergoes a change from the A conformation to the B conformation. As a result, new interactions between subunits are established and the affinities of the vacant sites change. K represents a dissociation constant. Thus, if the affinities of vacant sites increase, a, b, and c (the interaction factors) are <1 and we observe positive cooperativity (a sigmoidal velocity curve). The sequential interaction model also provides for, negative cooperativity (a, b, and c are > ). (o ) Dimer model. The two ways of arranging S to form a singly-occupied species is shown, (fe) Tetramer model. For simplicity, only one arrangement of each occupied species is shown.

For example, the products of decay of phenoxyl radical in aqueous solutions are 80% C—C dimerization products, 10% C—O dimerization products and 10% were not identified, possibly including some peroxide products. The major group of products includes 2,2 -, 2,4 - and 4,4 -dihydroxybiphenyl with ratios of 0.7 1.7 1.0. The second group includes both 2- and 4-phenoxyphenol. The relative abundance of the various products does not correspond to the relative spin populations at the oxygen and the various carbon atoms and... 

Serum concentrations of o-dimer, a by-product of thrombin generation, usually are elevated. 

Figure 12. Variation of the proportions of the three ferric components as a function of water content (T = 4.2 K, 23 Fe3+/100 SOs-). Key , isolated ions O, dimers , larger groups.

Figure 34. The structure of QAFGIO [Ho(C5H604)(phen)Cl], where l,10-phenanthroline = phen.l,10-Phenanthroline chelates Ho—O dimers that are then connected through glutarate groups to form chains along [100]. The large phenanthroline groups also participate in n stacking.

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