Theoretical Investigations on Fluorine‐Substituted Ethylene Dications C2HnF4‐n2+(n = 0–4)

Abstract

AbstractThe optimized geometries and energies of fluorine‐substituted ethylene dications C2HnF4‐n 2+ (n = 0–4) have been investigated by means of ab initio methods. At the MP3/6‐31G**//6‐31G* + zero‐point energy level of theory, the results predict that C2F42+ and C2HF32+ are planar, while C2H42+, C2H3F2+ and 1,1—C2H2F22+ prefer a perpendicular geometry. For 1,2—C2H2F22+ an energy difference of only 0.3 kcal/mol is found between the (trans) planar and perpendicular structure. The stabilizations attributed to hyperconjugation, fluorine lone‐pair donation, and (CF) double‐bond conjugation are discussed. A comparison is made for the CC and CF stretching frequencies determined at 6‐31G*//6‐31G* between the neutral and dicationic species. The theoretically determined ionization energies for the vertical process N+ → N2+ at the MP3/6‐31G*//3‐21G level are compared with experimental Qmin values.