THE EFFECT OF ELECTRON-DONATING AND ELECTRON-WITHDRAWING SUBSTITUENTS ON H-1-NMR AND C-13-NMR CHEMICAL-SHIFTS OF NOVEL 7'-ARYL-SUBSTITUTED 7'-APO-BETA-CAROTENES

The synthesis of 7'-aryl-7'-apo-beta-carotenes, where aryl (Ar) is Ph, 4-NO2C6H4, 4-MeOC6H4, 4-(MeO2C)C6H4, C6F5, and 2,4,6-Me3C6H2, is described. NMR Chemical shifts of all H- and C-atoms are presented, together with specific examples of the spectra. In contrast to H-1 chemical shifts which, except for H-C(8') and H-C(7'), did not differ greatly from those of beta,beta-carotene, considerable variations in C-13 chemical shifts were observed. Signals of the C(alpha) atoms of the polyene chain [C(beta)=C(alpha)]n Ar were shielded, those of the C(beta) atoms were deshielded, with some exceptions when n = 1; the effects decreased with increasing n.