Quantum-mechanical calculation of the structural and energetic characteristics of the fluorinealcanes

Abstract

Within the «quantum theory of atoms in molecules» the charge q and volume V of topological atoms A and atomic groups R of fluorinated molecules of ethanes C2HmFk, where 0 ≤ m, k ≤ 6 and m+k = 6 and propanes C3HmFk, where 0 ≤ m, k ≤ 8, m+k = 8, has been calculated by Aimall software package. Optimization of the geometry and finding of the electron density distribution (ρ(r)) has been carried out by the GAUSSIAN 03 program with the B3LYP 6-311++G (3df,3pd) 6d 10f level of theory. Influence of fluorine atoms on near atomic groups has been studied. The absence of the transferable functional groups has been showed. A conclusion has been made about unsuitability of the evaluation of properties by additive methods, which do not consider differences in electron structures for this class of compounds. The enthalpy of formation ΔfH0 of 38 molecules of fluorethanes and fluorpropanes has been computed by the G4 method. The comparison with the experimental values has shown good coherence. Results of this work is planned to be used in designing additive models for prediction of thermodynamic and thermochemical properties of organic fluorinated compounds.

Keywords

• inductive effect
• electronegativity
• electron structure
• enthalpy of formation
• quantum theory of atoms in molecules
• electron density
• fluorine alkanes
• fluorethanes
• fluorpropanes