Azides molecular geometry

The possibility of ring closure was expected to depend on molecular geometry. Thus, photolysis of n-propyl azide (7) in cyclohexane produced only the imine (8) in 59% yield, isolated as the 2,4-dinitro-phenylhydrazone (9). Irradiation of phenylethyl azide (10) resulted... 

Scheiner has shown that triazolines undergo both direct and sensitized photoelimination of molecular nitrogen to yield aziridines.463 With the triazolines prepared from phenyl azide and cis- or trans-fi-methylstyrene, direct photolysis produces a mixture of aziridines in which the starting geometry has been largely retained. Sensitized photolysis, however, is totally nonstereospecific. 

The reactivity of pyrylium ions with azides has been discussed theoretically on the basis of extended Hiickel molecular orbital (EHMO) calculations (84T3549). As long as the pyrylium ring is hindered, the most favorable approach of the reactants corresponds to a reaction coordinate yielding azidopyrans. However, when the ring approach is free, the system can assume a geometry that allows the formation of a stable complex. 

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