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Conformational properties of C 2 v ‐symmetrical resorcin[4]arene tetraethers
Author(s) -
Morikawa Osamu,
Iyama Eiichi,
Oikawa Tomoyoshi,
Kobayashi Kazuhiro,
Konishi Hisatoshi
Publication year - 2006
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1023
Subject(s) - chemistry , intramolecular force , hydrogen bond , resorcinol , ether , calixarene , nuclear magnetic resonance spectroscopy , stereochemistry , spectroscopy , crystallography , molecule , organic chemistry , physics , quantum mechanics
Resorcin[4]arene tetraether derivatives, in which a resorcinol unit and a 1,3‐dialkoxybenzene unit are incorporated in an alternating order, were synthesized by the Sc(OTf) 3 catalyzed ‘2 + 2’ fragment condensation. The conformational properties were studied using variable temperature 1 H‐NMR spectroscopy, indicating that the resorcinarenes are flexible at room temperature but frozen in the cone formation at −90 °C in CD 2 Cl 2 , and they interconvert between two equivalent cone conformations with an energy barrier of ΔGc‡ = 10.2–10.5 kcal mol −1 . These values are slightly lower than that for the resorcin[4]arene containing four 2‐hexylresorcinol units. The cone conformation is stabilized by intramolecular hydrogen bonds between the OH hydrogen and ether oxygen, which is evidenced by the low frequencies (3423–3434 cm −1 ) of the OH‐stretching vibrations in CDCl 3 solution. Copyright © 2006 John Wiley & Sons, Ltd.