AIM study on the influence of fluorine atoms on the alkyl chain

A topological analysis of HF/6-31++G(**)HHF/6-31G(*) electron distributions on diverse conformers of 36 linear fluoroalkanes of formula CHnF3-n(CH2)(m)CH3 was carried out within the atoms in molecules (AIMs) formalism. Group energy additivity of molecular energies was found in spite of lack of energy transferability. Cooperative effects due to stepwise fluorination on carbon I that appear to be around to 90 kJ mol(-1) according to traditional analysis based upon fitted group energies, exceed 370 U mol-1 when obtained from AIMs energies. Mean values of atomic properties and empirical relationships between concrete atomic properties lead to a definition of transferable fragments. It was found that the effect of fluorine atom on the chain is appreciable at further carbons for trans than for gauche arrangements, whereas effects on the hydrogen atoms give rise to an oscillatory behaviour (related to F-H interatomic distances) displayed along the whole chain. (C) 2002 Elsevier Science B.V. All rights reserved.