A comparative study on a series of penta-O-alkylated p-H-calix[5]arenes 1b-e and p-tert-butylcalix[5]arenes1g-m shows that the former are inherently mobile and adopt in solution non-cone conformations. The 1,2-alternate conformation for penta-O-benzyl ether 1c was proven by single-crystal X-ray analysis. VT-NMR studies on 1c-e have provided the first experimental evidence that conformational interconversion occurs via the p-phenyl-through-the-annulus mechanism with ΔG‡ in the range 17.9–18.8 kcal mol−1. Unlike the corresponding tert-butylated counterparts, p-H-calix[5]arenes are unable to form 1:1 endo-calix complexes with primary unbranched alkylammonium cations.
Influence of the size of upper and lower rim substituents on the fluxional and complexation behaviour of calix[5]arenes
NOTTI, Anna;PARISI, Melchiorre;
1998-01-01
Abstract
A comparative study on a series of penta-O-alkylated p-H-calix[5]arenes 1b-e and p-tert-butylcalix[5]arenes1g-m shows that the former are inherently mobile and adopt in solution non-cone conformations. The 1,2-alternate conformation for penta-O-benzyl ether 1c was proven by single-crystal X-ray analysis. VT-NMR studies on 1c-e have provided the first experimental evidence that conformational interconversion occurs via the p-phenyl-through-the-annulus mechanism with ΔG‡ in the range 17.9–18.8 kcal mol−1. Unlike the corresponding tert-butylated counterparts, p-H-calix[5]arenes are unable to form 1:1 endo-calix complexes with primary unbranched alkylammonium cations.Pubblicazioni consigliate
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