Photochemical Substitution Reactions in Synthetic Organic Chemistry

5 Photochemical Substitution Reactions in Synthetic Organic Chemistry 

Photoexcited aromatic compounds undergo substitution reactions with (non-excited) nucleophiles. The rules governing these reactions are characteristically different and often opposite to those prevailing in aromatic ground state chemistry 501a,b , in contrast to the well known ortho/para activation in thermal aromatic substitutions, nitro groups activate the meta position in the photochemical substitution, as shown in (5.1) 502). 

3-Halogenopyridines can be photohydrolized efficiently. The quantum yield of photohydrolysis is independent of the pH-value (5.2) 501 a . 

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