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N ‐(4‐Phenylbutyl)azacalix[3.1.1.1]arene: Self‐Inclusion of the Side Chain through CH···π Interactions
Author(s) -
Takemura Hiroyuki,
Yonebayashi Yuka,
Nakagaki Takeshi,
Shinmyozu Teruo
Publication year - 2011
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201001460
Subject(s) - chemistry , conformational isomerism , substituent , intramolecular force , supramolecular chemistry , methylene , molecule , stereochemistry , side chain , ring (chemistry) , crystallography , chain (unit) , nuclear magnetic resonance spectroscopy , medicinal chemistry , organic chemistry , physics , polymer , astronomy
Azacalixarene 1 , with a relatively long chain substituent, can exhibit both inter‐ and intramolecular CH ··· π interactions. In the crystalline state, the 4‐phenybutyl group is included in the molecular cavity, allowing interactions between the methylene H atoms and the aromatic rings of the azacalix skeleton. In addition, similar “edge‐to‐face” interactions occur between the terminal phenyl ring and that of an adjacent molecule, thus forming a polymeric, supramolecular array of azacalixarene molecules. In solution, the 4‐phenylbutyl arm adopts two orientations, one included in the calix cavity, one not, giving rise to isomers describable as exo and endo conformers. Characterization of the exo / endo equilibrium as a function of temperature by 1 H NMR spectroscopy enabled estimation of the enthalpy difference favoring inclusion attributed to the intracavity CH ··· π interactions.