Theoretical investigation of some N-nitrosodiphenylamine biological molecules - A natural bond orbital (NBO) study

Theoretical study of several N-nitrosodiphenylamine biological molecules has been performed using quantum computational ab initio RI-IF and density functional B3LYP and B3PW91 methods with 6-311G++(d,p) basis set. Geometries obtained from density functional theory (DFT) calculations were used to perform Natural bond orbital (NBO) analysis. The p characters of two nitrogen natural hybrid orbitals (NHOs) sigma(N3)-(N2) increase with increasing sigma(p) values of the substituents on the benzene, which results in a lengthening of the N3-N2 bond. The p characters of oxygen NHO sigma(O1)-(N2) and nitrogen NHO sigma(O1)-N-2 bond orbitals decrease with increasing sigma(p) values of the substituents on the benzene, which results in a shortening of the N2=O1 bond. It is also noted that decreased occupancy of the localized sigma(N3)-(N2) orbital in the idealized Lewis structure, or increased occupancy of sigma(*)(N3)-(N2) of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are also related to the resulting p character of the corresponding nitrogen NHO of sigma(N3)-(N2) bond orbital.