(13)C CP MAS NMR study of some 4,4'-disubstituted-trans-azobenzenes

Azobenzenes with para-dimethylamino group at aromatic ring and various para substitutes to another phenyl have been studied by (13)C CP MAS NMR spetroscopy followed by semi-empirical AMI MO calculations. The locked trans-configuration around N=N bond in the state results in non-equivalence of ortho carbons (C2 and C6, also C2' and C6') and the diference in chemical shifts is 12.9-22.0 ppm. The separation of meta carbons resonances is less manifested but in 1, 3, 4, 8 the non-equivalence of C3' and C5' is enhanced by the orientation of X-substituents at C4'.