Based on a starting point of the McWeeny Huckel-London perturbation theory approximation, a formula similar to the fourmula of additivity rule for the calculations of the chemical shifts of condensed aromatic hydrocarbons has been derived. The quantum mechanical basis of additivity rule is thus indicated by this formula. It is shown that by using the concept of aromatic shift and sigma ratio, this method for calculation of proton chemical shifts has the virtues of definite physical meaning and simple calculation. It can also be extended to the calculation of the proton chemical shifts of substituents fr the molecules of this series.

Key words: AROMATIC HYDROCARBON, CALCULATION, NMR SPECTROMETRY, CHEMICAL SHIFT, PERTURBATION THEORY, POLYNUCLEAR AROMATIC HYDROCARBON, FUSED RING COMPOUNDS, QUANTUM MECHANICS