ELECTRONIC-STRUCTURES OF TRIFLUOROMETHANE, TRICYANOMETHANE, AND TRINITROMETHANE AND THEIR CONJUGATE BASES

The electronic structures of CHF3, CH(CN)3, and CH(NO2)3 and their conjugate bases are studied at thc HF/6-31G* and HF/6-31++G** levels of theory. Topological features of the electron densities in the systems under study are interpreted within the framework of Bader's theory of atoms in molecules. The observed changes in geometry, the electron densities at the critical points, and the GAPT charges reveal the presence of Y-aromaticity in the C(CN)3- and C(NO2)3- anions. Unusual weak bonds between the oxygen atoms belonging to different nitro groups in the C(NO2)3- anion are found. Absolute gas-phase acidities (proton affinities of the conjugate bases) are computed. There is no correlation between the acidities and any of the following molecular indices: the length and the stretching force constant of the C-H bond, the topological parameters of the C-H bond point, the Bader and GAPT atomic charges of the hydrogen atoms in the neutral molecules or of the carbon atoms in either neutral molecules or the corresponding anions. The GAPT charges appear to provide a better description of the electron density redistribution upon deprotonation than the Bader ones.