From nonpolar to polar: the reconstruction mechanism of electronic structure in alkane C–C bonds induced by fluorine substitution

Abstract

Context

The C–C bonds in alkanes are generally considered nonpolar covalent bonds, but the mechanism by which fluorine substitution affects the polarity and cleavage mode of C–C bonds in alkanes remains unclear. In this study, using 1,1,1-trifluoroethane (CH₃-CF₃) as a model, we systematically investigated the reconstruction mechanism of the electronic structure of C–C bonds induced by fluorine substitution through density functional theory calculations, combined with bond critical point (BCP) topological analysis, atomic charge calculation, and flexible scan simulation. The results demonstrate that fluorine substitution transforms the C–C bond into a polar covalent bond via a strong electron-withdrawing inductive effect, leading to the separation of positive and negative charges on the two carbon atoms and breaking the nonpolar symmetric distribution. Flexible scan simulations reveal that the C–C bond cleavage in CH₃-CH₃ follows a typical covalent bond homolysis, whereas that in CH₃-CF₃ exhibits ionic bond characteristics. This study uncovers the reconstruction mechanism of C–C bonds from nonpolar to polar induced by fluorine substitution and its disruptive impact on the bond cleavage pathway, providing a theoretical basis for understanding the structure–property relationships of complex fluoroalkanes.

Methods

All quantum chemical calculations adopted the M06-2X functional paired with the Def2-TZVP basis set. Initial molecular structures were built in GaussView, with geometry optimization performed via Gaussian 16 to obtain optimized configurations and wavefunction files. Wavefunction analyses (including BCP topology, Hirshfeld atomic charge, Mayer bond order, and spin population/density calculations) were conducted using Multiwfn.

Graphic Abstract