The halogen•••oxygen interaction in 3-halogenopropenal revisited - The dimer model vs. QTAIM indications

Even though a bond path and the corresponding bond critical point were found for the intramolecular X center dot center dot center dot O (X = Cl, Br) interaction in 3-halogenopropenal, thus according to QTAIM suggesting the stabilizing nature of this interaction, it was shown that this contact is repulsive. In order to utilize the well-defined energy of the intermolecular interaction, a dimer model was used. The C-X center dot center dot center dot O=C fragment from the ZZ conformer of 3-halogenopropenal was preserved with its original geometrical arrangement. Such approach leads to the conclusion according to which the presence of a bond path and the corresponding bond critical point do not necessarily indicate a stabilizing interaction between a pair of atoms, but rather is a direct consequence of a large accumulation of the electron density between atoms. Values of QTAIM parameters characterizing both BCP of X center dot center dot center dot O and RCP remain rather unchanged if the C-X center dot center dot center dot O=C fragment with its preserved geometry is embedded in a dimer. It was also shown that atoms X and O are interacting by negative surfaces of the molecular electrostatic potential. Also the charge transfer between interacting fragments is opposite to expected. (C) 2013 Elsevier B.V. All rights reserved.