Ionic disproportionation

The complexes react photochemically with ligands to form ionic disproportionation products (e.g., eq. 17). 

Ionic disproportionation of NO can be promoted in non-polar media by the addition of Bronsted acids and Lewis acids [10]. The photochemical activation of the nitrosonium donor-acceptor complex via irradiation of the charge-transfer absorption band produces the aromatic radical cation. The most direct pathway to aromatic nitration proceeds via homolytic coupling of the aromatic radical cation with NO [16] because the intermediate subsequently undergoes very rapid deprotonation ... 

Photochemical Reactions in Solution. Metal-metal bonds react photochemically in solution according to one of three fundamental types of reactions (4). (1) They react with radical traps to form monomeric complexes (e.g., equation 10) (2) they react with ligands to form ionic disproportionation products (e.g., equation 11) and (3) they react with oxygen to form metal oxides (equation 12). (lie latter reaction is likely a radical trapping reaction in the sense that an oxygen molecule reacts with a photogenerated metal radical.)... 

Write a balanced net ionic equation for foe disproportionation reaction... 

Chain reactions do not continue indefinitely, but in the nature of the reactivity of the free radical or ionic centre they are likely to react readily in ways that will destroy the reactivity. For example, in radical polymerisations two growing molecules may combine to extinguish both radical centres with formation of a chemical bond. Alternatively they may react in a disproportionation reaction to generate end groups in two molecules, one of which is unsaturated. Lastly, active centres may find other molecules to react with, such as solvent or impurity, and in this way the active centre is destroyed and the polymer molecule ceases to grow. 

It has also been shown that the disproportionation reaction, with the generation of the ionic componnd from thioamide-iodine complexes, exhibits pressure dependence [2]. A pressnre increase, leads to the ionic iodonium salt (iii) from (ii) (Scheme 13.2). The favouring of [MBZIM) ] [I3] (24a) formation, is also proven by compntational stndies, based on energetic gronnds [6]. 

Write the net ionic equation and the half-reactions for the disproportionation of mercury(I) ions in aqueous solution to give liquid mercury and aqueous mercury(II) ions. Assume that mercury(I)... 

Complete and balance a net ionic equation for each of the following disproportionation reactions. 

The analogy between electron-transfer via addition/elimination (Eq. 2b,c) or abstraction/elimination (Eq. 2a, c) and classical solvolysis involving closed-shell molecules (nonradicals) is seen by comparing Scheme 1 with Scheme 3, in which XY, the precursor of the ions X and Y , is formally derived from the two radicals X and Y". Analogous to Scheme 1, on the way to the ionic products that result from the interaction between X and Y there are two possibilities if XY denotes a transition state, the reaction (Eq. 3a, a ) is a case of outer-sphere electron transfer. If, however, a covalent bond is formed between X and Y, the path (Eq. 3b, b ) is an example of inner- sphere electron transfer. Obviously, part b of the scheme describes the classical area of S l solvolysis reactions (assuming either X or Y to be equal to C) [9, 10]. If a second reaction partner for C (other than the solvent) is allowed for (the (partial) ions then represent transition states), then Eq. 3b also covers Sn2 reactions. If looked upon from the point of view of radical-radical reactivity, Eqs. 3a and b show well-known reactions radical disproportionation in Eq. 3a,a and combination in Eq. 3b. 

Critical appraisal of the method, 23,26 using attempts to synthesize nonsymmetrically substituted lanthionines, resulted in rearrangement of the products, presumably due to phosphine-catalyzed disproportionation of the unsymmetrical disulfides. This reaction should proceed more rapidly than the desulfurization process and is thought to occur because sulfur extrusion takes place via a reversible reaction by recombination of ionic intermediates (Scheme 3). 21-22-24 Thus, the reaction of nonsymmetrical cystine derivatives results in the formation of a mixture of three different lanthionines. 

Generally, the reduction is achieved under deaerated conditions to avoid a competitive scavenging of Cjoiv and H atoms by oxygen. These atoms are as homogeneously distributed as the ions and the reducing species, and they are therefore produced at first as isolated entities. Similarly, multivalent ions are reduced by multistep reactions, including disproportionation of intermediate valencies. Such reduction reactions have been observed directly by pulse radiolysis for a variety of metal ions (Fig. 2), mostly in water [28], but also in other solvents where the ionic precursors are soluble. Most of their rate eonstants are known and the reactions are often diffusion controlled. 

The determination of equilibrium (standard) potentials is rather problematic for several reasons for instance, hydrolysis and disproportionation reactions, the existence of a large number of structural forms (e.g. a-, fi-, y-, 5-Mn02), strong dependence on pH and ionic exchange processes, and the instability of the species in contact with water (e.g. Mn-metal-hydrogen evolution, Mn04 oxygen evolution however, these processes are rather slow). 

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