Effect of substituents on the 1H n.m.r. spectra of para-disubstituted benzenes. A graphical aid in the correct assignment of chemical shifts

In para-disubstituted benzenes, the effect of one substituent is transferred to the other composite substituent group and its decreased influence on the ortho and meta protons is reflected in their chemical shifts. A graphical presentation of this linear non-additive dependence can serve as an aid in the correct assignment of the corresponding aromatic region of the spectra. The method is demonstrated on two series of chemical shift data taken from the literature.