Premium
Syntheses and conformations of persubstituted inverse calixarenes
Author(s) -
Schätz Rolf,
Weber Christian,
Schilling Gerhard,
Oeser Thomas,
HuberPatz Ursula,
Irngartinger Hermann,
von der Lieth ClausW.,
Pipkorn Rüdiger
Publication year - 1995
Publication title -
liebigs annalen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0947-3440
DOI - 10.1002/jlac.1995199508190
Subject(s) - calixarene , chemistry , intramolecular force , benzene , crystallography , stereochemistry , molecule , nuclear magnetic resonance spectroscopy , organic chemistry
A series of ten inverse calix[ n ]arenes (2–11) bearing four to thirteen benzene units were prepared by starting from 3,4,5‐trimethoxybenzaldehyde followed by LC separation on silica gel. In 2–11 the substitution pattern is interchanged compared with the usual calixarenes. The conformational analysis was undertaken by variable temperature 1 H‐NMR spectroscopy and by MM2 calculations. Calix[4]arene 2 is a rigid molecule and shows the 1,3‐alternate conformation which in addition was proven by X‐ray analysis. At low temperatures the calix[5]arene 3 adopts the uudod conformation, where a methyl group of one benzene unit residues in the cavity of the macrocycle. At low temperature calix[6]arene 4 forms an 1:2 equilibrium between the 1,3,5‐alternate (ududud; 4E ) and the uududu (4B) conformation. Conformation 4B can be regarded as an intramolecular combination of a cone and an alternate arrangement of the benzene units. The calix[8]‐arene shows the highest Δ G * value of the series and adopts an uuududdd conformation at low temperature. The inverse calixarenes 5 and 7–11 bearing seven and nine to thirteen aromatic units, respectively, are conformationally highly flexible systems even at low temperatures.