Chemical interpretation of molecular electron density distributions

In this study, the two small molecules HS(CH)(CH2), 1, and F(CH)(4)F, 2, are presented, which yield different chemical interpretations when one and the same density is interpreted either by means of Natural Bond Orbital and subsequent Natural Resonance Theory application or by the Quantum Theory of Atoms In Molecules. The first exhibits a S-C bond in the orbital based approach, whereas the density based Quantum Theory of Atoms In Molecules detects no corresponding bond. In F(CH)(4)F a F center dot center dot center dot F bond is detected in the density based approach, whereas in the orbital based approach no corresponding bond is found. Geometrical reasons for the presence of unexpected and the absence of expected bond critical points are discussed.