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Hydrogen Bonding versus H−H Interactions in Pillar[n]arenes
Author(s) -
Athare Sulakshana V.,
Gejji Shridhar P.
Publication year - 2019
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201901984
Subject(s) - conformational isomerism , cavitand , hydroquinone , hydrogen bond , crystallography , chemistry , methylene , density functional theory , stereochemistry , molecule , computational chemistry , supramolecular chemistry , crystal structure , medicinal chemistry , organic chemistry
We employ the ωB97x based density functional theory to explore the electronic structure and bonding features of macrocyclic hosts composed of hydroquinone aromatic units endowed with pillar‐like structure, namely the pillar[n]arenes (Pn, n=5–8, 10, 12) family. It has been shown that Pn (n=5–7) possess single‐cavitand structure. The stability of P5‐P7 hosts is governed by C−H−O cooperative hydrogen bonding. A gradual decrease in C−H−O cooperative hydrogen bonding along the P5–P7 series was noticed. The homologated Pn (n=8, 10, 12) hosts on the other hand, favour the conformer wherein the methylene groups at the bridging position orient mutually at an angle of ∼64° which engender a noncavitand structure which can be attributed to H−H interactions prevailing over C−H−O cooperative hydrogen bonding. Besides P8 and P10 hosts furnish bi‐cavitand structures comprised of cavities with four and five monomeric hydroquinone units (P8–44 and P10–55) 42.9 kJ mol −1 and 79.7 kJ mol −1 higher in energy, respectively over their lowest energy twisted conformer. Moreover, P12 scaffold bicavitand conformers with (i) each cavity composed of six hydroquinone units (P12–66) and (ii) one cavity with seven and other with five hydroquinone units (P12–75) were also characterized. Unlike the lower Pn hosts H−H interactions contribute largely to the twisted conformers of Pn (n≥8) while cooperative CH−O hydrogen bonding dominates in their bicavitand structures. These inferences are corroborated through the Quantum Theory of Atoms in Molecules.