The planarity of heteroatom analogues of benzene: Energy component analysis and the planarization of hexasilabenzene

There are various nonplanar heteroatom analogues of benzene—cyclic 6π electron systems—and among them, hexasilabenzene (Si6H6) is well known as a typical example. To determine the factors that control their planarity, quantum chemical calculations and an energy component analysis were performed. The results show that the energy components mainly controlling the planarity of benzene and hexasilabenzene are different. For hexasilabenzene, electron repulsion energy was found to be significantly important for the planarity. The application of the pseudo Jahn–Teller effect and the Carter–Goddard–Malrieu–Trinquier model for the interpretation of the planarity of the benzene analogues was also investigated. Furthermore, based on the quantitative results, it was revealed that the planarization of hexasilabenzene is realized by introducing substituents with π‐accepting ability, such as the boryl group, that bring about a reduction of the π‐electron repulsion on the silicon skeleton. © 2018 Wiley Periodicals, Inc. Hexasilabenzene (Si6H6) is well‐known as a typical example of nonplanar heteroatom analogues of benzene. The present study shows that the energy factors mainly controlling the planarity of benzene and hexasilabenzene are different. Based on the quantitative results, some strategies to systematically control the planarity of hexasilabenzene, such as utilizing the substituent effect, are suggested.