Natural bond orbital (NBO) population analysis of some benzyl nitrites

Abstract

Theoretical study of several benzyl nitrites have been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with 6-31G∗∗ basis set. Geometries obtained from DFT calculations were used to perform NBO analysis. It is noted that weakness in the O₃–N₂ sigma bond is due to $n_{\text{O}1}\to {\sigma }_{\text{O}3''–''\text{N}2}^{\ast }$ delocalisation and is responsible for the longer O₃–N₂ bond lengths in the selected benzyl nitrites. It is also noted that decreased occupancy of the localized ${\sigma }_{\text{O}3''–''\text{N}2}$ orbital in the idealized Lewis structure, or increased occupancy of ${\sigma }_{\text{O}3''–''\text{N}2}^{\ast }$ 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 (NHO) of ${\sigma }_{\text{O}3''–''\text{N}2}$ bond orbital. In addition, the charge transfer energy decreases with the increasing of the Hammett constants of substituent groups.