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Blue‐Shift Hydrogen Bonds in Silyltriptycene Derivatives: Antibonding σ* Orbitals of the Si−C Bond as Effective Acceptors of Electron Density
Author(s) -
Mames Adam,
Gołowicz Dariusz,
Pietrzak Mariusz,
Kazimierczuk Krzysztof,
Szymański Sławomir,
Ratajczyk Tomasz
Publication year - 2020
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201901141
Subject(s) - antibonding molecular orbital , chemistry , natural bond orbital , triptycene , crystallography , atomic orbital , hydrogen bond , electron deficiency , covalent bond , computational chemistry , density functional theory , atom (system on chip) , non covalent interactions , hydrogen atom , electron density , group (periodic table) , electron , molecule , organic chemistry , physics , quantum mechanics , computer science , embedded system
Abstract Triptycene derivatives are widely utilized in different fields of chemistry and materials sciences. Their physicochemical properties, often of pivotal importance for the rational design of triptycene‐based functional materials, are influenced by noncovalent interactions between substituents mounted on the triptycene skeleton. Herein, a unique interaction between electron‐rich substituents in the peri position and the silyl group located on the bridgehead sp 3 ‐carbon is discussed on the example of 1,4‐dichloro‐9‐( p ‐methoxyphenyl)‐silyltriptycene (TRPCl) which exists in solution in the form of two rotamers differing by dispositions, syn or anti, of the Si−C Ph (the C Ph atom is from the p ‐methoxyphenyl group) bond against the peri‐Cl atom. For the first time, substantial differences between the Si−C Ph bonds in these two dispositions are identified, based on indirect experimental and direct theoretical evidence. For these two orientations, the experimental 1 J(Si,C Ph ) values differ by as much as 10 percent. The differences are explained in terms of effective electron density transfer from the peri‐Cl atom to the antibonding σ* orbitals of the Si−X bonds (X=H, C Ph ) oriented anti to that atom. The electronic effects are revealed by an NBO analysis. Connections of these observations with the notion of blue‐shifting hydrogen bonds are discussed.