Mesomeric dipole moments. Part 12

The dipole moments of para-substituted azoxybenzenes (1, a-e) and phenylazoxycyanides (2, a-e) were analyzed in terms of bond moments and additional contributions expressing electron delocalization. The results are compatible with a significant participation of the polar mesomeric formula B (25% or 34% for1 and2, respectively), the N-O bond acquiring considerable double-bond character. Comparison of known x-ray structures reveals that this bond is significantly shortened, whereas the N=N bond is extended only very slightly. Hence we can consider the possibility that the N1 atom allocates somewhat more than eight valence electrons, similarly to nitro compounds. In all respects the properties of the azoxy group are between those of the nitro and imino-N-oxide groups.Part 11 appears in Exner, O.J. Phys. Org. Chem.1990,3, 190.