ELECTRON PARAMETERS OF 1,1,1 - TRILUOROALKANES

On the basis of quantum-chemical calculations the properties of trifluoro-substituted hydrocarbon molecules CnH2n+1-CF3 (n <= 9) received from their electron density distribution were considered. The geometry optimization of ten structures was carried out. The surfaces of zero flow electron charge density gradient were specified, and the basins of atomic groups and fluorine atoms were found. The electron integral parameters (charges q(R), energies E(R) and volumes V(R)) of atomic groups in trifluoroalkane molecules were calculated and analyzed. The relationship between the length of the hydrocarbon chains and the transferability of the properties of the selected groups (CF3, CH3, CH2) was revealed, that is reflected in their transferable parameters. For the studied homologous series the qualitative group electronegativity scale was made up and inductive effect (I - effect) of fluorine containing group was considered. The attenuation of I - effect in CnH2n+1-CF3 (n >= 6) within molecular fragments CF3-(CH2)(4) and CH3-CH2 was identified. In this regard, the appearance of the "unperturbed" CH2 group was registered at n > 6. The "standard" (or "transferable") value of the total group energy E(R) was introduced and computing of the relative group energy Delta E(R) was described. It was shown, that the reduction of the volumes of the nearest CH2 to the CF3 was caused by the electron density redistribution. The comparative analysis of the group charges q(R) in CnH2n+1-CF3 (n <= 9) with corresponding q(R) in monofluorine alkanes, monofluorine alkane radicals, difluorine alkanes and difluorine alkane radicals was performed. The comparison of the charges of relevant groups and fluorine-containing fragments of the fluoro-substituted nonane and their radicals was presented as graphic dependence, which provides an understanding of the attenuation of I - effect from CF3.