Abstract: In the light of resonance theory,an empirical method has been put forward in this paper.Let Ki be the parameter for the calculation of resonance theory,where i corresponds to the various Kekulè's formulae. The contributions to Ki of sextet benzene ring,the ring only with con-jugated diene inner the ring itself,as well as the ring without the above conditions,are 2,1 and 0,respectively.If the experimental resonance energy of benzene is R,and the Kekulè structure count is SC,then the resonance energy of the corresponding benzenoid polycyclic aromatic hydro-carbonds may be obtained by the following equation:
RE=(R)/(2)???19860208???K_i²/???19860208???K_i
The calculated values approximate highly to the experimental values,and have excellent linear correlation with the calculated values by SCF-MO and other methods.The method is named as benzene ring count method by this author.Based upon this BRC method,9 general equations for the acene, phene,starphene series and the derivated acene series have been established.The RE_BRCshow excetlent linear correlation with the experimental K₂ of Diels-Alder reaction.