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

Azobenzenes with para-dimethylamino group at aromatic ring and various para substituents to another phenyl have been studied by C-13 CP MAS NMR spectr oscopy followed by semi-empirical AM1 MO calculations. The locked trans-con figuration around N=N bond in the solid state results in non-equivalence of ortho carbons (C2 and C6, also C2' and C6') and the difference 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 enhance d by the orientation of X-substituents at C4'.