The Photoreduction of Aryl Ketones Structural Aspects

So far in this chapter we have discussed only the photoreduction of benzophenone. We will now concern ourselves with the effect of structure on the photoreduction of aromatic ketones in general. 

The following three carbonyl compounds are photoreduced in isopropyl alchohol as solvent or in the presence of benzhydrol  

On the other hand, the foOowing compounds do not undergo photoreduction under these conditions  

The question is, what difference (or differences) is responsible for the fact that photoreduction occurs in the first group of compounds but not in the second There are four possible reasons for this behavior. We shall deal with each of these in turn and attempt to decide whidi factor is responsible. 

Possibly for those compounds that do not photoreduce the triplet does not have enough energy to abstract a proton to form the ketyl radical. To explore this possibility, one must look at the overall energetics of the abstraction reaction. 

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