Article ID Journal Published Year Pages File Type
5280205 Tetrahedron Letters 2009 4 Pages PDF
Abstract
Tetranitroazacalix[4]arenes have been synthesized by the nucleophilic aromatic substitution of 1,5-difluoro-2,4-dinitrobenzene with 1,3-diaminobenzenes. An X-ray crystal structure analysis revealed that the azacalixarenes adopt a non-symmetrical 1,3-alternate conformation, and the dinitrobenzene rings strongly conjugate with the bridging nitrogen atoms. In the 1H NMR spectrum (CDCl3, 30 °C), the tetraisopropyl derivative 3b displays a pair of diastereotopic methyl signals of the isopropyl groups in agreement with the frozen 1,3-alternate conformation on the NMR time scale. The free energy of activation (ΔG298≠) for the macrocyclic inversion was determined to be 87.5 kJ mol−1 by temperature-dependent NMR spectroscopy.
Related Topics
Physical Sciences and Engineering Chemistry Organic Chemistry
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