Reactivity linkage isomerization

Most of the available information about the reactivity of CTTM excited states comes from studies of Cora acidoammines.91 92 Typically, irradiation of a CTTM absorption band in these systems leads to efficient redox decomposition accompanied, in many cases, by ligand substitution or linkage isomerization. The behavior of a representative complex, [CoC1(NH3)5]2+, is summarized in equation (39).93 A common observation in these systems is that photoredox quantum yields increase at shorter excitation wavelengths and decrease with increasing solvent viscosity.91 92... 

The polymerization of five- and six-membered cyclic imino ethers including the substituted ones, goes usually to completion (cf. Table 12-1). In addition to the relief of ring strain, the driving force of these polymerizations is the isomerization of the reactive imino ether linkages (—N=[Pg.210]

Phenol-formaldehyde resins are produced by a system of chemical reac tions in which the linkage of phenol molecules by meth dene groups plays a predominant part. How ever, because of the rapidity nith Yhich con-ieeutive phenol-formaldehyde reactions usually take place, the isolation d simple methylene derivatives containing onb two or three phenolic nuclei is often extremely difficult. This is particularlj true of phenols in which the active oi tho and para positions are unsubstituted and in which pnups which tend to lower reactivity, such as nitro and carboxyl radicals, are absent. Since in these cases a large number of simple isomeric products can be formed, the separation of any one isomer in a pure state is difficult. The isolation of the simple methylene derivatives is noteworthy, since it clarifies our knowledge of the mechanism by which the more complicated products are produced. 

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