Decomposition and Isomerization of Bridgehead Cis 1,2-Diazenes (Azoalkanes)

Article abstract of DOI:10.1021/ja00406a026

Four acyclic cis 1,2-diazenes, azo-1-adamantane (cis-ada), azo-bicyclo<2.2.2>octane (cis-<2.2.2>), azo-1-bicyclo<2.2.1>heptane (cis-<2.2.1>), and azo-1-bicyclo<2.1.1>hexane (cis-<2.1.1>) have been generated by UV irradiation of the corresponding trans-isomers.These compounds differ greately in stability, cis-<2.1.1> easily surviving at 100 deg C and cis-ada not being isolable.Whereas cis-<2.1.1> and cis-<2.2.1>only isomerize back to trans on heating, the other two compounds undergo competing loss of nitrogen.The observation that the energy of the transition state for isomerization remains at 42 +/- 1 kcal mol^-1 regardless of the cis ground state energy is used to argue that thermal isomerization proceeds via semilinearization rather than rotation.A remarkable correlation of cis ground state energy with cis n,?^* excitation energy has emerged from this study.