dft study of nmr shielding tensors and thermodynamic properties on pyrene and its derivatives

emissions from fossil fuel combustion pose a serious threat to public health and =pose the need for animproved monitoring of polycyclic aromatic hydrocarbons (pars), a major class of persistent organicpollutants. for this purpose the present study reports an investigation of the electronic structure of pyrene byuse of different chemical models we also made a comparison between different chemical models.donor — acceptor disubstituted , entropy , enthalpy and gibbs free-energy vall be compared too.the isotropic and anisonopic tensor of the pyrene and derivatives structure were calculated with differentchemical models hp/6-3ig, hf/m1-3 l0, blyp/6-3 id, blyp/6-310. , b3lyp/a3 ig, b3lyp.16-3 i 00 and aswell.