Polybrominated dibenzofurans (PBDFs)are important toxic organic contaminants released from the combustion and Pintsch process of brominated flame retardants.The properties of PBDFs are related to their structures.The structure of polybrominated dibenzothiophenes (PBDTs)is similar to that of PBDFs.In this study

atomic characteristic values of 254 molecular structural patterns of PBDEs and PBDTs are calculated

and a new connectivity index

the path index

is obtained by applying the technique of molecule graphics.The path index is combined with five thermodynamic properties of PBDFs

including molecular total energy (ET)

standard enthalpy (H0)

free energy (G0)

standard entropy (S0)and heat capacity at constant volume (c0v)

along with four thermodynamic properties of PBDTs

including standard enthalpy (H0)

free energy (G0)

standard enthalpy of formation (ΔfH0)and standard free energy of formation (ΔfG0）.Nine quantitative structure-property relationship models (r2>0.995)are obtained by multiple linear regression method.The Jackknifed cross validation is used to test the stability and prediction ability of each model and good results (r2>0.995)are obtained.The relative mean deviation is 0.52% to S0.The model developed is in good agreement with the values of S0 in literature.