Influence of laterally attached alkyl groups on the conformational behaviour of a basic calix[4]arene: combined NMR, molecular mechanics and X-ray study

Gruner, Margit and Fischer, Conrad and Gruber, Tobias and Weber, Edwin (2010) Influence of laterally attached alkyl groups on the conformational behaviour of a basic calix[4]arene: combined NMR, molecular mechanics and X-ray study. Supramolecular Chemistry, 22 (4). pp. 256-266. ISSN 1061-0278

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Item Type:Article
Item Status:Live Archive

Abstract

Three new calixarenes 3–5 featuring an alkyl residue of different chain lengths attached to one of the central ring methylene groups of the basic calix[4]arene 1 have been prepared. A systematic study that includes also the lower homologous compound 2 showing the effect of the alkyl substitution on the conformational behaviour of the calixarene framework in comparison with the unsubstituted parent compound 1 is reported. The application of special 2D NMR techniques, 2D-EXSY and ROESY methods at various temperatures establishes that calixarenes 2–5 adopt the partial cone conformation of lower symmetry and far less the symmetric cone and 1,2-alternate conformations. In solution, they undergo a fast interconversion with relatively low activation energies of about 15 kcal/mol at room temperature. The conformer distribution is well reproduced by molecular mechanistic calculations (MMFF94), indicating the present conformers to assume the lowest steric energies. A single-crystal X-ray structure of the lateral ethyl derivative 2 corroborates these results, showing the molecule in a sterically favourable partial cone conformation.

Keywords:calixarene, cyclophane, Molecular Conformation, Organic synthesis
Subjects:F Physical Sciences > F160 Organic Chemistry
Divisions:College of Science > School of Pharmacy
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ID Code:20029
Deposited On:14 Jan 2016 22:10

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