Natural bond orbital population analysis of para-substituted O-nitrosyl carboxylate compounds

Theoretical study of several para-substituted O-nitrosyl carboxylate compounds has been performed using density functional B3LYP method with 6-31G(d,p) basis set. Geometries obtained from DFT calculation were used to perform natural bond orbital analysis. It is noted that weakness in the O₃–N₂ sigma bond is due to $ n_{{{\text{O}}_{1} }} \to \sigma_{{{\text{O}}_{3} - {\text{N}}_{2} }}^{*} Theoretical study of several para-substituted O-nitrosyl carboxylate compounds has been performed using density functional B3LYP method with 6-31G(d,p) basis set. Geometries obtained from DFT calculation were used to perform natural bond orbital analysis. It is noted that weakness in the O₃–N₂ sigma bond is due to n_\textO1 ? s_{\textO3 - \textN2} ^* n_{{{\text{O}}_{1} }} \to \sigma_{{{\text{O}}_{3} - {\text{N}}_{2} }}^{*} delocalization and is responsible for the longer O₃–N₂ bond lengths in para-substituted O-nitrosyl carboxylate compounds. It is also noted that decreased occupancy of the localized s_{\textO3 -\textN2} \sigma_{{{\text{O}}_{3} --{\text{N}}_{2} }} orbital in the idealized Lewis structure, or increased occupancy of s_{\textO3 - \textN2} ^* \sigma_{{{\text{O}}_{3} - {\text{N}}_{2} }}^{*} of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are related with the resulting p character of the corresponding sulfur natural hybrid orbital of s_{\textO3 -\textN2} \sigma_{{{\text{O}}_{3} --{\text{N}}_{2} }} bond orbital. In addition, the charge transfer energy decreases with the increase of the Hammett constants of substituent groups and the partial charges distribution on the skeletal atoms may approve anticipating that the electrostatic repulsion or attraction between atoms can give a significant contribution to the intra- and intermolecular interaction.