Origin of Hydrocarbons Stability from a Computational Perspective: A Case Study of Ortho‐Xylene Isomers

Abstract

It is shown herein that intuitive and text‐book steric‐clash based interpretation of the higher energy “in‐in” xylene isomer (as arising solely from the repulsive CH⋅⋅⋅HC contact) with respect to the corresponding global‐minimum “out‐out” configuration (where the clashing C−H bonds are tilted out) is misleading. It is demonstrated that the two hydrogen atoms engaged in the CH⋅⋅⋅HC contact in “in‐in” are involved in attractive interaction so they cannot explain the lower stability of this isomer. We have proven, based on the arsenal of modern bonding descriptors (EDDB, HOMA, NICS, FALDI, ETS‐NOCV, DAFH, FAMSEC, IQA), that in order to understand the relative stability of “in‐in” versus “out‐out” xylenes isomers one must consider the changes in the electronic structure encompassing the entire molecules as arising from the cooperative action of hyperconjugation, aromaticity and unintuitive London dispersion plus charge delocalization based intra‐molecular CH⋅⋅⋅HC interactions.

Supramolecular structures of NiII and CuII with the sterically demanding Schiff base dyes driven by cooperative action of preagostic and other non-covalent interactions

“…Although they contain the prevailing dispersion constituent, the charge-delocalization contribution is only slightly less important followed by the Coulomb term. Our results, clearly showing that the bulky cyclohexyl groups are the sources of London dispersion stabilization, are in line with the recent discoveries outlining the true character of steric effects in small and sizable species (Cukrowski et al, 2016;Liptrot & Power, 2017;Mitoraj et al, 2019dMitoraj et al, , 2020Wagner & Schreiner, 2015). Furthermore, we have determined that intramolecular…”

“…Although they contain the prevailing dispersion constituent, the charge-delocalization contribution is only slightly less important followed by the Coulomb term. Our results, clearly showing that the bulky cyclohexyl groups are the sources of London dispersion stabilization, are in line with the recent discoveries outlining the true character of steric effects in small and sizable species (Cukrowski et al, 2016;Liptrot & Power, 2017;Mitoraj et al, 2019dMitoraj et al, , 2020 ÁE int = ÁE Coulomb + ÁE XC , where ÁE int is the overall diatomic interaction energy, ÁE Coulomb is the Coulomb constituent and ÁE XC is the exchangecorrelation contribution (Blanco et al, 2005). IQA energy decomposition of the selected diatomic interactions obtained at the MP2/6-311 + G(d,p) level of theory for the crystal monomers of [Ni(L I,II ) 2 ] and [Cu(L I,II ) 2 ] (see Table 4 for details).…”

“…The existence of a stabilizing charge-delocalization channel (XC) for such ultra long distance OÁ Á ÁH is also an important observation. It has been additionally supported by the ETS-NOCV results where the mentioned intramolecular charge-delocalization channels in addition to C-HÁ Á ÁH-C (Cukrowski et al, 2016;Liptrot & Power, 2017;Mitoraj et al, 2020;Wagner & Schreiner, 2015) have been discovered ( Fig. S6).…”

“…S6). Recently, the latter has been of particular attention in terms of reconsidering the real nature of steric crowding in bulky species (Cukrowski et al, 2016;Liptrot & Power, 2017;Mitoraj et al, 2020;Wagner & Schreiner, 2015). Notably, substitution of L I by L II leads to a similar picture of the already discussed intramolecular non-covalent interactions (Fig.…”

Zeolites at the Molecular Level: What Can Be Learned from Molecular Modeling

“…Such extracted bonding channels formed between a metal active center and a ligand are useful for in-depth understanding of the origin of IR red-shift in stretching CC frequencies due to metal-ligand bonding. It has also been shown that ETS-NOCV is suitable for the reliable description of various non-covalent interactions [92,93].…”