N2 Elimination from Azo Compounds

The lowest excited state of many azo compounds, like that of ketones, is an (n, r ) state. Photolytic cleavage of a CN bond analogous to the a cleavage of ketones is therefore to be expected  

Another conceivable route would be the concerted elimination of nitrogen  

Experimental data and theoretical arguments indicate that the concerted path is energetically unfavorable, so in general the two-step mechanism is involved (Engel, 1980). 

For most acyclic azo compounds photodissociation in solution is an indirect process, that is, the photochemical reaction proper is a trans-cis isomerization, and the c -azoalkane formed undergoes thermal decomposition to nitrogen and radicals. This occurs especially if the cis isomer is suffi- 

The use of triplet sensitizers has shown that the major part of direct photolysis does not involve the triplet state the extrusion of nitrogen from the triplet state requires an activation energy E, (Engel, 1980). 

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