Photochemical Reactions in Solution

The qualitative photochemistry of the polymers in solution is analogous to the reactions of the discrete metal-metal bonded dimers in solution. As in the photochemical reactions of the dimers, the photochemical reactions of the polymers can be conveniently monitored by electronic absorption spectroscopy. The quantum yields for the reactions are in the range 0.1 to 0.6, depending on the specific polymer and the M-M bond. Sample reactions of the polymers showing the three types of reactivity are shown in eqs. 18-20. 

As mentioned, a fourth type of dimer reactivity is dissociation of a CO ligand from the dimer. Generally, this type of reactivity increases in efficiency relative to M-M photolysis as the radiation energy increases. In solution, this type of reactivity generally leads to substitution. However, in the case of the Cp2Mo2(CO)6 molecule, the reaction in equation 21 occurs. (Among the dimers, this reaction to form a triply bonded product is unique to the Mo and W species.) 

In both equations 21 and 22, addition of CO to the product solution causes the system to back-react to reform the starting materials. Once again, the main point to be made is that the solution photochemistry of the polymers is analogous to the solution photochemistry of the discrete metal-metal bonded dimers. 

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Among the first things that one should know about a photochemical reaction in solution is the order of the reaction with regard to the concentration of all of the reacting species, and with regard to the... 

Asymmetric Photochemical Reactions in Solution Simon R. L. Everitt and Yoshihisa Inoue... 

Herkstroeter, W. G., A. A. Lamola, and G. S. Hammond Mechanisms of photochemical reactions in solution. XXVIII. Values of triplet excitation energies of selected sensitizers. J. Amer. chem. Soc. 86, 4537 (1964). 

Kristinsson, H. and Hammond, G.S. (1967) Mechanisms of photochemical reactions in solution. XLVIII. rearrangement of phenylvinylcyclo-propanes. Journal of the American Chemical Society, 89, 5970-5971. 

Photochemical reactions in the solid state may also go to limited conversion when the product does not compete for incident light but may act as an efficient energy quencher. This is likely to be of importance in triplet state reactions when the product may act as an energy trap. Although this is a factor that may also limit the conversion of photochemical reactions in solution, because of efficient energy delocalization by dipole-dipole and exchange mechanisms it is likely to be more important in the crystalline solid state. 

Recently a number of reviews have appeared,9 22 63 72 76 84 98 which deal with photochemical reactions in solution. This reflects the great attention this subject is receiving at present from all branches of chemistry. Any elucidation of the mechanisms of photochemical reactions must in-... 

Template-Induced Enantioselective Photochemical Reactions in Solution... 

As shown below, the enantiomeric excess achieved in the 6n-cyc-lisation reaction of amide 22 to the tetrahydrophenathridinone 23 remained below 60% ee. While this is still an impressive value for a photochemical reaction in solution, the observed enantiomeric excess is clearly inferior to the values achieved in the different photochemically induced cycloaddition reactions presented in Sect. 2.2 and Sect. 2.3. As pointed out previously, complete chirality transfer from the template to the substrate is only possible if a complete complexation of the sub-... 

Grosch B, Bach T (2004) Template-induced enantioselective photochemical reactions in solution. In Inoue Y, Ramamurthy V (eds) Molecular and supramolcular photochemistry, vol 11 Chiral Photochemistry. Dekker, New... 

Grosch, B., Bach, T., Template induced Enantioselective Photochemical Reactions in Solution. In Inoue, Y., Ramamurthy, V. (eds), Chiral Photochemistry, Vol. 11, Marcel Dekker, New... 

Lamola, A. A., and G. S. Hammond Mechanism of Photochemical Reactions in Solution XXIII Intersystem Crossing Efficiences. J. Chem. Phys. 43, 2129 (1965). 

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