No abstract

The Charge‑Charge Flux‑Dipole Flux (CCFDF) model in terms of multipoles from the quantum theory of atoms in molecules (QTAIM) was used to investigate the variations in infrared intensities of hydroxyl (OH) stretching modes during the dimerization of carboxylic acids. The hydrogen bond formation in these systems results into bathochromic shifts of vibrational frequencies for all the OH stretching modes along with huge infrared intensity increments for some of them. These bands become more intense on dimerization due mainly to changes in the cross‐term contribution between charge and charge flux. In addition, interaction energies for the pair of atoms directly involved in individual hydrogen bonds (O…H) are linearly correlated to electron densities at their bond critical points (BCPs). Therefore, the hydrogen bonds between the carbonyl group (CO) of acetic acid and the hydroxyl group of halogenated monomers show the largest electron density values at their BCPs. The formation of these intermolecular interactions is also accompanied by ionic character enhancements of OH bonds and electron density decrements at their BCPs. We finally noticed that the hydrogen atom belonging to the hydroxyl group loses electronic charge, while the oxygen from the CO end becomes more negatively charged during dimerization. © 2019 Wiley Periodicals, Inc.

In order to evaluate the substituent effect on the reactivity and regioselectivity of aromatic rings with respect to electrophilic substitution reactions, we considered several benzene derivatives containing activating (ÀNH 2 , ÀNHCH 3 , ÀN(CH 3 ) 2 , ÀOH, ÀOCH 3 , and ÀCHCH 2 ) and deactivating (ÀF, ÀCl, ÀBr, ÀCOH, ÀCOCH 3 , ÀCOOCH 3 , ÀCOOH, ÀCOCl, ÀCN, and ÀNO 2 ) groups. In this sense, we propose alternative theoretical descriptors of reactivity and regioselectivity, which are based only on electron density properties of initial substrates. The descriptors investigated here were obtained from the quantum theory of atoms in molecules (electron density curvatures at the ring critical point [RCP] and at the critical points of carbon nuclei along with kinetic and potential energy densities at the RCP) and from the interacting quantum atom formalism (intra-atomic energy values of carbon atoms). The topological parameters at the RCPs and at carbon nuclei within the aromatic moiety were particularly successful in this task, being able to provide quantitative predictions of reactivity as compared with traditional resonance parameters used to that same end.

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