Generalizing the Breakdown of the Maximum Hardness and Minimum Polarizabilities Principles for Nontotally Symmetric Vibrations to Non-π-Conjugated Organic Molecules

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2005-02, Vol.109 (4), p.615-621
• Main Authors: Torrent-Sucarrat, Miquel, Duran, Miquel, Luis, Josep M., Solà, Miquel
• Format: Article
• Language: English
• Subjects: Aluminum - chemistry; Anions - chemistry; Borohydrides - chemistry; Computer Simulation; Hardness; Models, Molecular; Molecular Structure; Organic Chemicals - chemistry; Stereoisomerism; Vibration
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp0470804

In previous works we have shown that certain π-conjugated organic molecules possess nontotally symmetric vibrations that break the maximum hardness (MHP) and minimum polarizability principles (MPP). We have also derived a set of simple rules to determine a priori without calculations whether a particular π-conjugated organic molecule violates these two principles. In the present work, we generalize these results, and we show that not only π-conjugated organic molecules but also other molecules without π-conjugated structure or even π-bonds can exhibit nontotally symmetric molecular distortions that do not follow these two principles. We have also found that the breakdowns of the MHP and the MPP are not necessarily connected, since the polarizability is not always proportional to the softness. Finally, we also introduced a methodology based on the diagonalization of the hardness Hessian matrix with respect to the vibrational normal coordinates to determine the nontotally symmetric molecular displacements that do not follow the MHP.