Do Linear-Chain Perfluoroalkanes Bind an Electron?

Abstract

The adiabatic electron affinities (AEAs), vertical electron affinities (VEAs), and vertical detachment energies (VDEs) of linear-chain perfluoroalkanes (PFAs), n-CnF2n+2 (n = 2−8) are predicted using carefully calibrated computational methods (Chem. Rev. 2002, 102, 231). Density functional theoretical methods and hybrid Hartree−Fock/density functional methods have been used with double-ζ-quality basis sets with polarization and diffuse functions, DZP++. Vibrational frequency analyses were performed to compute the zero-point energy corrections and determine the nature of the stationary points. The estimated adiabatic electron affinities of linear-chain PFAs (CnF2n+2), from n = 3 to n = 8, turn out to be appreciable, ranging from 0.26 to 0.58 eV (B3LYP/DZP++ method). The corresponding zero-point-corrected values are a bit larger, ranging from 0.39 to 0.71 eV. C2F6 is the only n-PFA exhibiting a negative adiabatic electron affinity. The trends in AEAs of the n-PFA show that the AEA increases with increasing chain length until n = 7 and then slightly decreases at n = 8. The VEAs of all the linear chain PFAs are negative. VEAs increase with increasing length of the linear-chain PFAs. The VDEs indicate that all the straight-chain PFA anions considered are bound with respect to electron loss. It was also observed that PFA molecules show enhanced AEAs when they are branched. The presence of tertiary C−F bonds in PFAs results in high AEAs compared to those of their straight-chain counterparts.