Abstract: In the present paper the calculation methods of chemical shifts of protons in the rings of fused benzenoid aromatic hcterocyclics and their alkyl chains has been proposed.
The chemical shift of fused benzenoid aromatic helerocyclics must be presented by KeKul'e formulas, the calculation formula is:
σ_j,c=c are the effects of ethenyls in the benzene rings that must be calculated.σ_mi,Cj are the net ring-current effects of benzene rings.σ_l,Hc are shielding effects of aromatic heterocyclics. If the proton belongs to an aromatic heterocyclic ring,σ_l,Hc is chemical shift of the proton that is in the same position of the single aromatic heterocyclic ring. If the proton belongs to benzene rings,σ_l,Hc must be divided into the effects of the structural units, thus:
σ_l,Hc=(1/2)^d-1σ_x=y(or σ_z)+σ_c-c+σ_m,Hc σ_x=y and σ_Z are shielding effects ofheteroatom or hcteroatomic group +σ_c-c is the effect of ethenyl if it is situated in the aromatic heterocyclic ring. σ_m,Hc is net ring current effect of aromatic helerocyclic ring, d is the bond number that is concerned to the different protons. The substituting groups must be considered if they are present. The calculation fomula for the protons of alkyl chains in a ring is:δσ_P,CH3+α σ_S,CH3+β σ_t,CH3+σ_i,G σ_i,G is a certain order effect of fused benzenoid aromatic heterocyclic radical.